Hi. If you look back, I was here in April asking these same questions. The problem was never resolved, I just resigned myself to using Dropbox online instead of the App,
The problem is only on my Windows 10 laptop which I reset in April (Dropbox was working fine on it before the reset). I have two other PCs, a W10 and a W11, both use Dropbox perfectly well. My Android mobile phone also uses the app without any difficulty. I have the basic Dropbox account so I understand that if I want more than 3 devices to use the app I have to log one off first. All my devices are on the same router and home network so if one works they all should.
I've tried everything that has been suggested in this thread and nothing has helped.
It would be great to find a solution, but I'm pessimistic.
Sue