Nathan Explosion

Yes - you likely have your tasks set to use CRON (check that in the ACP), and the command line for your CRON entry needs to be updated to reflect the version of PHP you are using (check that on your hosting)

Got DEBUG_TEMPLATES in your constants? Try removing it.

On this tab - scroll down
 

Do those clicking the link have permissions to 'Download attachments'?
The behaviour you see is because anyone is allowed to view the video, because it's a direct link to the .mov file and no check is done on permissions there. But the fallback to the attachment.php file does do a permissions check.
Been that way since 4.3 was released:
 
 

.ipsCode{ height:250px; overflow:scroll; }  

The field 'Title' uses a language string called 'topic_title', so you could edit that language string instead?
Alternatively....there is no language string called 'topic_title_desc' so you could take advantage of that - I've sent you a plugin xml file that literally does only that.
Note: if IPS decided to implement that language string themselves at a later point, you would need to disable the plugin before upgrading to whatever version it is that introduces the language string, otherwise you might end up with an issue during upgrade.

In Clubs -> Settings...

It does the same for Plugins...


Requirements:
It's a Marketplace installed plugin (just like applications) OR
If it is custom, then the author has to have populated the "Update Check URL" value of their resource so that when they release a new version, there is a URL that can be checked to see what the next version is (requires that the author has also updated that item that it being checked)

You are not editing a JS file - you should be editing the globalTemplate in your theme.
 

There's your issue right there - use PHP7.4.x, 8.0.x or 8.1.x

Define 'reset'...do you simply want to delete the content that is in the stream, as opposed to the stream itself?

$record->truncated(false, 100);

It would be more beneficial to turn off "Post before registering" instead, which allows guests to begin creating a post, and leave it sitting there ... which I believe then triggers that email out to them to remind them to finish off the submission.

Go to the support page in your ACP and you should see optional patches available to fix this.

In that case you'll likely have to use the cookie you mentioned (which expires after 3 months)
That gives you the user's ID, and you could then use the REST API to get more information about that user.

Go into your ACP, click the bell and I am pretty sure there is a notification setting for that.

They should click 'Notification Settings' and see what is set for the relevant item - if "No Notification List" then no notification...

In your acp, type display name into the search bar and click on 'allowed display name length'

Go here: https://invisioncommunity.com/clients/purchases/
Click the 'manage' button beside the item
Click 'Reactivate'

Give this a try - plugin instead of trying to write some javascript.
It will insert this:
<div class="popup" id="51f18_16504"></div> <script src="https://www.powr.io/powr.js?platform=html"> ...on every front-end page of your site, apart from the /login page.
(NE) Exclude _ hide script from loading in the login page 1.0.0.xml
Off to the pub now, back tomorrow.

All plugins are in applications\core\interface\ckeditor\ckeditor\plugins\ - custom ones are cunningly named custom-.......