the screen shot is for joomla 4 update server but you are referring to joomla 5

Yes Brian, I know that too, it was just an example of what it used to look like. You can recreate it yourself in 5.2.4 and you will see that no button is displayed anymore.

Since many Joomla 5.2.3 installations do not see updates for Joomla 5.2.4, this and the issue with the core files could be related. Until yesterday, updates for J5.2.4 were still being shown.

if your sites are not showing an available update you have a bigger problem than not being able to reinstall - something which you should almost never need to do at all

We manually installed the update to J5.2.4 for the affected customers and it worked without any problems.
Why is the update no longer displayed for so many of them?

No idea as I have no knowledge of your server - and how do you know it worked

Because we do updates every month and the last successful one was to 5.2.3. But it affects different hosts and not just one. Something has already been reported about this in the Joomla forum.

I'll now install a backup before 5.2.3 and check there again.

Something has already been reported about this in the Joomla forum.

@WM-Loose Can you please provide a link?

Yes: https://forum.joomla.de/thread/22210-update-auf-5-2-4-funktioniert-nicht/?postID=167221#post167221

Hey guys, have you changed anything now?
Customers have just received information that it is working again!
I have just tested it and Joomla updates to 5.2.4 are displayed.
The core files can now also be installed again if required, as the button now appears again.

So what was the cause of the problem? Update-Server?

update server has been fixed after a partly broken update for joomla 5.3.0beta2 yesterday