I changed my plan from Professional to Basic II and I can't find some files I'm sure I uploaded in 2023.
Any suggestions?
Dropbox does delete files if you are over quota for a long time - after multiple warnings via email, however. They are not just removed.
Have a look at www.dropbox.com/events to see if that gives any clues, however, if they are not on Dropbox now and not deleted in past 30 days they are not recoverable I'm afraid.