i am having this issue with a mac mini M1 - i am running the beta software that is supposed to work with the M1. I migrated data only using the migration assistant built into macs. Dropbox takes over my documents folder as soon as a sign in and the path changes showing it is now a dropbox folder - after doing a migration that folder is empty and if i restore to that folder the files disappear within a few minutes.
I am likely saying goodbye as i am fed up with poor mac support and poor support in general. I spent 4 hours chatting with their support people BEFORE i did the migration because i anticipated issues and sure enough the issues are real.