When I close files in Photoshop, Photoshop becomes unresponsive for about 3 seconds untils I can click anything again (menus, buttons ...). So If I want to close several images, I always have to wait for 3 seconds before I can close the next one. I went back to 21.0 but the problem seems to persist. So it might have to do with the recent Windows 10 2004 update. I'll investigate. But the weird thing is, that the problem only happens in Photoshop. No other apllications seem to be affected.
Edit: It wasn't the Windows Update either. It must have to do something with files. If I create a new image and immediately close it again, it's quick as usual. So it only happens when I work with physical files. I tried different harddisks, and it's the same on all drives. So it might not be harddisk related.
SOLVED: It was the Fontbase plugin that was installed without my knowledge when I installed Fontbase. Removing it from the Plugins directory solved the issue. I'll inform the creator. I'll also leave this thread online in case somebody experiences a similar problem.