Problems with files on my Mac - can anyone help?

Hey! I have a MacBook Air 2020 (Sequoia 15.0.1), I synchronise my data with iCloud. Recently a lot of files have been set to hidden (very randomly). At first I was surprised that the files had disappeared. Using a shortcut, I was able to show the files again. But they are still greyed out (the font is grey, not black like the other files). It affects files that are in the cloud, files that are not in the cloud, and all file types. I did not hide these files. How can I make my files permanently visible again? Why did this happen? Can anyone help me? Thank you very much.