app PREVIEW?

So where is that image filed? There is now a "sequestered", not accessible, read only volume on your Macintosh HD which contains the OS, system files, etc. If you parked it there, then no, you cannot edit/write to it.

Yes it does. Have you tried it with images or PDF documents?

I cannot unlock Preview in Big Sur, there is no option.

Preview is an application in your Applications folder. There is nothing to unlock.

Then when I open a jpg file does it say "locked". The ultimate problem is that I cannot copy that file into Photoshop and save it, because I don't have the "write access" as I did before Big Sur.