E11

I don’t remember any new feature to accomplish this so create a new stream, set it as default and choose all type of content, including topics, and use the option to narrow by forums and choose all forums, except the ones you don’t want their topics to be listed. All the other streams will remain showing these forums.
To mention only one disadvantage, you will have to remember to add new forums when you create them, otherwise they won’t show up in the stream.

Hmm, the code is basically trying to remove any birthday widgets and the table should already be there in theory since the core application upgrade is done. For now you can just open the file \applications\calendar\setup\upg_107305\upgrade.php and comment or remove this code on line 33:
\IPS\Widget::deprecateWidget('todaysBirthdays', 'calendar');  
As an aside, keep going with the upgrade until the end and once you're done I suggest you immediately restore a backup and redo the upgrade from scratch with all the fixes you've added so far already included.

Looks like the widgets table is not available but the code is trying to load it.
Can you take a screenshot just like the one above about the "Unfinished Upgrade"? That way we can see which step is throwing it.

Are those the only tables which start with "ibf_nexus_" ?
Also, using phpMyAdmin, please check the ibf_core_applications table.
Is there a record in it, with the app_title of "Nexus" ?

Have a look in the 'datastore' folder, the upgrader may have already generated some caches. If you see any PHP files in there, delete them and then try again.

The datastore folder is completely unrelated to the UTF8 converter, but since it's working now that's good. After deleting the table you would have needed to restart the UTF8 conversion.

Yeah, upgrading from 3.x can be as smooth as usual or tricky as hell depending on how many modifications were installed before the upgrade. When I do a legacy upgrade I usually uninstall as many modifications as possible beforehand. (As long as the client doesn't plan to upgrade them for 4.x.)
I've had issues with Tapatalk before, mainly because their code is well...let's just skip what I think of it. 😋
 
That error doesn't really help much though. There no file or line. You should probably have a more complete(?) error logged on the server.

Removing the /hooks folder won't change anything since the 4.x code doesn't even load the files inside it. That error is most likely from when you switched to PHP 8, but before uploading the files/running the upgrade.
 
That last screenshot indicates that the upgrade is stuck on a step for the gallery application (version 60000) so I initially thought the error must be coming from the file: \applications\gallery\setup\upg_60000\upgrade.php.
After taking a look there is no such reference to any array_keys() call in there though. Rather there is no such call at all in the whole \applications\gallery\setup folder. The error must be coming from some other file/function since it's also showing up when you try to access the ACP.
 
If you don't have a more complete error to look at, the only solution left would be to manually add debug code and find where exactly the code is throwing the error. While it looks like a bug, it's a bug from a 3.x upgrade so not sure if IPS would be able to help and take a look at it themselves. 🙄

The error may be because a variable isn’t declared hence the NULL. Probably there’s a conditional somewhere in that file that creates an array. As the condition returns FALSE, the error happens. That’s a PHP 8 thing. 
I would say the error is in the step 5. It’s enough to add $toRun = array(); before IF.
Just a guess. Not tested.

@Adriano Faria That's what I thought initially, but then I looked again at his other screenshot:
It's worth a try anyway.
 
Actually, scratch that. Taking a look again at the previous screenshot the issue there is with array_map() rather than array_keys(). They keys related one must be something else because the upgrade is not complete yet.
 
The only possible array_map() culprit in that upgrade file is on lines 236~239, it's the code that converts the image metadata from serialized to json format:
if( $row['image_metadata'] ) { $imageUpdate['image_metadata'] = json_encode( array_map( 'trim', unserialize( $row['image_metadata'] ) ) ); } The unserialize() function can indeed return a BOOL (false) value and the code is not accounting for that:
 
Try replacing the code above with this instead:
if( $row['image_metadata'] ) { $tmpMeta = unserialize( $row['image_metadata'] ); if( $tmpMeta === FALSE ) { $tmpMeta = array(); } $imageUpdate['image_metadata'] = json_encode( array_map( 'trim', $tmpMeta ) ); }  
Should be easy enough for IPS to add a fix in a future version even if they don't exactly support anymore upgrades from 3.x.

+Update,
the datastore is a 'drive me crazy' element.
The UTF convert process stopped at 14%, because it had an issue with converting Tapatalk tables.
As I dont need TT, I decided to remove all tables. Started the coverting processes again. Same problem after 14% was reached, Tapatalk was mentioned again as reason.
I followed Stuarts recommendation and cleaned the datastore - hey and voila, It worked as well

Assuming you have access to the database with phpMyAdmin or similar, check the list of tables in your database.
Are there any tables whose name starts with (assuming no table prefix is used), "nexus_" ?
If there are such tables, then nexus was either installed, or was attempted to be installed, at one point in the past, but then not removed properly. 

In that case, just remove the nexus folder and you should be able to proceed. 

(I would personally download a copy of it first just to be 100 percent safe!)

Nexus is now the Commerce app.  Do you still have that one associated with your license?

Hi @E11,
Really pleased you managed to upgrade your community!

For #1, if you've already changed the url in conf_global.php, then the home link is most likely hardcoded in the menu manager in ACP > System > SITE FEATURES > Menu Manager. Just edit the menu entry there.
 
For #2 & #3 instead you need to update your storage setting path in ACP > System > OVERVIEW > Files > Storage Settings (button top-right) > Configurations TAB.

From such an old version you'll need to upload the files, switch your server to PHP 8.0.x and run the upgrader from /admin/upgrade. Have a look at our guide here, specifically the 3.x section: 
 

Hrhrhr, that works. Yeah! 
Another step further. Thanks a lo for that Adlago. 
 
 
System says PHP Version 5.6.40 - any chance to initiate the upgrade process from ACP or is uploading the install package the only option?

Login ftp
Open .../admin/applications/core/modules_admin/mycp
and replace dashboard  php with
this
dashboard.php

After  {session key} add
&app=forums then Enter

You'll likely have a hard time getting it to work on anything newer than MySQL 5.5. You don't however need to be able to load the AdminCP to perform an upgrade. You can upload the new v4 files and go directly to the upgrade process.

Possible dashboard php issue
Try this - when you get this error after logging in ACP, in the browser command line, replace the command final from
&app=core
on
&app=forums
and Enter key
If this action gets you into ACP, I will send you a dashboard php to replace yours with.
 

Sorry, version 3 is no longer supported so I have moved this to our Community Support forum where fellow administrators can assist you.

That page means there is some kind of issue with a MySQL query or the MySQL server itself. It should save a log in the /cache folder and you can look up the actual error there.

Thanks for posting!

Unfortunately, this issue is beyond the scope of our technical support. 👩‍💻

Our technical support is happy to help you with the Invision Community platform, but we're unable to help with things like server management, theme questions and modifications.

I've moved this to our Community Support area where other Invision Community owners will see it and help where they can.