I send a big thank you to the author of this reply. He was the first to find the problem and provide a solution. I don't know why someone clicks "Likes" on replies that don't contribute much to the matter. Greetings to all.
I am having the same issue, just since the following Windows 10 update on Nov 1, 2024 ( a couple of days ago: 2024-10 Cummulative Update Preview.... Everytime I restart my computer, images from Explorer/all my files and folders, will open, but it is temporary each time. I also notice some updates with the Windows photos tool. So this must have been part of the update. This is obviously an update issue. Should I try to have Windows repair it or just uninstall the update? Hopefully a patch/updated update comes out quickly.
UPDATE 11/5/24: Found the issue, I think. The update just messed up the settings and removed it as the default app, leaving no app set. You need to readd Photos as the default. See screenshots...