Yamamura

I agree. But the mobile view needs additional changes.
1. There is no need to display pagination, and buttons "2", "3" and "4" make no sense at all. Seriously, who will click these buttons and why? 🤦🏻‍♂️

2. The words "replies", "view" and "updated" take up a lot of space and don't fit on one line in many localizations. They should be replaced with icons so as not to interfere with viewing and to save space.
Before:

After:

No wonder. Most people are stupid and lack an understanding of good design.

OMG 😱🤣😭

I totally agree. The default skin in 4.5 is absolutely terrible. Huge elements, padding, empty space, thin and faded text, low contrast, and more. It's no surprise why more and more people are choosing to use XenForo, Discord, etc., over IPB. I don't know who made the new skin, but it feels like a beginner freelancer from Dribble made it.
But why did they need to move the follow button one line down? If the follow button was positioned on the same line as the title, as before, there would be no useless empty space.
One more example:

It takes up a lot of space, but none of it is needed there.
You just entered a topic and want to reply right away? Not! You just entered a topic and want to create a new topic right away? Of course not!  Who cares who is the author of the topic and when it was created? Nobody! For example, I have active topics on my forum that are already 12 years old. Why should I constantly show who is the author of these topics if they have not visited the forum for 10 years and everyone has already forgotten about them?? Nobody cares who is the author of the topic. This information is completely meaningless and useless. One more example:

Am I exactly in a place for people to communicate? Because on my screen I see only a white space and a couple of lines of text. 🤦🏻‍♂️

I totally agree. The default skin in 4.5 is absolutely terrible. Huge elements, padding, empty space, thin and faded text, low contrast, and more. It's no surprise why more and more people are choosing to use XenForo, Discord, etc., over IPB. I don't know who made the new skin, but it feels like a beginner freelancer from Dribble made it.
But why did they need to move the follow button one line down? If the follow button was positioned on the same line as the title, as before, there would be no useless empty space.
One more example:

It takes up a lot of space, but none of it is needed there.
You just entered a topic and want to reply right away? Not! You just entered a topic and want to create a new topic right away? Of course not!  Who cares who is the author of the topic and when it was created? Nobody! For example, I have active topics on my forum that are already 12 years old. Why should I constantly show who is the author of these topics if they have not visited the forum for 10 years and everyone has already forgotten about them?? Nobody cares who is the author of the topic. This information is completely meaningless and useless. One more example:

Am I exactly in a place for people to communicate? Because on my screen I see only a white space and a couple of lines of text. 🤦🏻‍♂️

'set it and forget it' and remember 12 months later to pay $10 again.

Will this be fixed in the next versions of Invision Community or do I need to buy a plugin for $ 10.00 / 12 months for this primitive feature?

'set it and forget it' and remember 12 months later to pay $10 again.

When using facebook logins you had to have a facebook developer account and create a facebook app so that's nothing new, not sure why IPS can no longer support oEmbed,
Once again a developer has stepped in and restored the feature back so quickly, not knocking the developer of the plugin. They all have my respect and thanks for restoring dropped features or improving the IPS software. Thank you all
At this particular time i have to stop buying plugins as they all total up per year and start to make the software expensive.    

I can take a screenshot of forum 4.4 where everything was fine.
Lol!

Why did they move the follow button to a separate line, which takes up a HUGE white space??? Previously, this button was in the title bar and did not take up extra space. Read "Web Design For Dummies" before commenting here.

Maybe a toggle button to enable compact view in all categories / topics of the forum?

I've had it for several years on 4.4

When a site administrator gets used to not leaving "harmless" mistakes, ie. not to compromise - then this administrator will find any resource that creates a delay. There are too many methods to overcome delays on the net.
For example - image preload, especially for mobile performance, "onload" of other images, font preload, etc.
Of course, different cross-tests should be performed each time such techniques are used. This is a necessity because sometimes an improvement is good for a desktop, but it is bad for mobile performance, and so on.
The process of loading speed analysis is time consuming enough to be underestimated. There is enough work on everything a site uses - before applying acceleration techniques.

But this is precisely why there is a responsive layout - so that the page looks equally good on different devices and different screen sizes.
But I feel there is a lot of space here that can be saved.

Why are all the elements so huge? This is not a touch screen. Why do you pay so much attention to secondary elements there (highlighted in red), dropping the main content to the bottom of the page? Author / date creation. I wrote about the author and the date of creation here. Follow. Forums with thousands of members and millions of posts, but several people subscribe to topics. It looks something like this: Promote. Who sees this button? Only admins and moderators? So it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Share. Do you have statistics on the use of this button? This button is almost never used by anyone, but you have given it a central place on the page. Seriously? Moderation Actions. Again — so it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Start new topic / Reply. I wrote about it here. One more example on a smartphone:

It looks ugly, it duplicates the same action, it interferes with clicking the "Submit" button.

But this is precisely why there is a responsive layout - so that the page looks equally good on different devices and different screen sizes.
But I feel there is a lot of space here that can be saved.

Why are all the elements so huge? This is not a touch screen. Why do you pay so much attention to secondary elements there (highlighted in red), dropping the main content to the bottom of the page? Author / date creation. I wrote about the author and the date of creation here. Follow. Forums with thousands of members and millions of posts, but several people subscribe to topics. It looks something like this: Promote. Who sees this button? Only admins and moderators? So it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Share. Do you have statistics on the use of this button? This button is almost never used by anyone, but you have given it a central place on the page. Seriously? Moderation Actions. Again — so it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Start new topic / Reply. I wrote about it here. One more example on a smartphone:

It looks ugly, it duplicates the same action, it interferes with clicking the "Submit" button.

But this is precisely why there is a responsive layout - so that the page looks equally good on different devices and different screen sizes.
But I feel there is a lot of space here that can be saved.

Why are all the elements so huge? This is not a touch screen. Why do you pay so much attention to secondary elements there (highlighted in red), dropping the main content to the bottom of the page? Author / date creation. I wrote about the author and the date of creation here. Follow. Forums with thousands of members and millions of posts, but several people subscribe to topics. It looks something like this: Promote. Who sees this button? Only admins and moderators? So it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Share. Do you have statistics on the use of this button? This button is almost never used by anyone, but you have given it a central place on the page. Seriously? Moderation Actions. Again — so it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Start new topic / Reply. I wrote about it here. One more example on a smartphone:

It looks ugly, it duplicates the same action, it interferes with clicking the "Submit" button.

But this is precisely why there is a responsive layout - so that the page looks equally good on different devices and different screen sizes.
But I feel there is a lot of space here that can be saved.

Why are all the elements so huge? This is not a touch screen. Why do you pay so much attention to secondary elements there (highlighted in red), dropping the main content to the bottom of the page? Author / date creation. I wrote about the author and the date of creation here. Follow. Forums with thousands of members and millions of posts, but several people subscribe to topics. It looks something like this: Promote. Who sees this button? Only admins and moderators? So it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Share. Do you have statistics on the use of this button? This button is almost never used by anyone, but you have given it a central place on the page. Seriously? Moderation Actions. Again — so it only looks good to a few people on the forum, but thousands of other members see a huge empty space? Start new topic / Reply. I wrote about it here. One more example on a smartphone:

It looks ugly, it duplicates the same action, it interferes with clicking the "Submit" button.

I do receive the newsletters (I avoid corporate social media as far as possible). Nothing I had read thus far indicated such dramatic under the hood changes to me. 
Bottom line for me right now is that I am stuck here on 4.5 and having to use a default theme that I personally think looks awful and I can't find an easy way to change it. Even my premium theme doesn't let me easily make the changes I was used to making. 
Just really disappointed in the design aesthetic and the fact that it's so hard to change now. 
I suggest that in future it might be advisable to split your communications into categories that deal with the aesthetics changes as well as the functional changes. But then again, we're being forced to upgrade, so even if we don't like what we see in new versions there's not much we can do about it if we want to keep support current. 

It's good to know that people are listening, but this doesn't save those of us who don't follow every development move that IPS makes from wasting literal days when we update in good faith only to find that regression has occurred instead of progression. 
I'm fighting with aesthetics now for 2 full days and it seems I'll be doing so for days to come still because tweaking custom CSS now seems to involve an entirely different approach to what I am used to (inspect element in Safari is not showing me things I am familiar with). 
Honestly, this isn't good looking and I truly regret doing this upgrade, but those front end upgrade notices were really starting to annoy me. 😞 

Have to chip in here in agreement with the OP. 
I've been using IPS since 2011 if memory serves me well and this update from an aesthetic stance is horrible. I don't even use the default theme but I can tell from 2 days of trying to get Taman's Behemoth back to where I had it at 4.4 that the changes that have been made to layout are not an improvement over 4.4. My opinion of course.
I have had to use a coloured variation of the default theme while I get Behemoth working and so far user feedback hasn't been positive. 
I'm not seeing anything I like about 4.5 aesthetically to be honest. 

It's Full HD. The main content is marked in green. More than half of the screen at the top is occupied by secondary useless information.

And if we use a logo with a large header, then the main content will generally be at the very bottom of the page.

I totally agree. The default skin in 4.5 is absolutely terrible. Huge elements, padding, empty space, thin and faded text, low contrast, and more. It's no surprise why more and more people are choosing to use XenForo, Discord, etc., over IPB. I don't know who made the new skin, but it feels like a beginner freelancer from Dribble made it.
But why did they need to move the follow button one line down? If the follow button was positioned on the same line as the title, as before, there would be no useless empty space.
One more example:

It takes up a lot of space, but none of it is needed there.
You just entered a topic and want to reply right away? Not! You just entered a topic and want to create a new topic right away? Of course not!  Who cares who is the author of the topic and when it was created? Nobody! For example, I have active topics on my forum that are already 12 years old. Why should I constantly show who is the author of these topics if they have not visited the forum for 10 years and everyone has already forgotten about them?? Nobody cares who is the author of the topic. This information is completely meaningless and useless. One more example:

Am I exactly in a place for people to communicate? Because on my screen I see only a white space and a couple of lines of text. 🤦🏻‍♂️

I agree with most of the criticisms here; way too much whitespace. I understand some of the design choices were to allow other applications to insert bits of UI, but there should be better ways to approach it than "placeholders just in case".
Discourse is a good example; I wish I had their UX but this backend .

Wow, I love this minimalistic quoting that doesn't take up space:


Invision is so dated 😞

I didn't realize how much space was being utilized until I switched to 4.5. This is kind of a lot I agree 😂 
I would love to somehow simplify this so it's about 75% shorter in length. For instance, it says the author and time stamp twice.
 

At least as user, I say IPS need a little more innovative investment in UI, CONTENT VS SPACE, maybe Flarum can be an example, not have to do same, but learn the good of others and improve mine is part of a success...