Okay, I've done all of this now. I even completely uninstalled and reinstalled Everything and let it run with default settings.
It still doesn't show thumbnails and previews for images. Actually, there are no thumbnails nor previews for any file types.
Is there anything else I could try?
Attached is the debugging log.
I only noticed that shutting down Everything via the tray icon does not work. It remains active with two processes in Task Manager. When I then start Everything, this prompt appears after a minute or so:
If I click on Terminate, Everything then comes up again.
Also, I have tried to save all settings files so that I would be able to restore them after the reinstallation. Unfortunately, some settings are missing, for example my customized $openpath("%1") command. In which file would this be saved?