I have the same issue. When I disabled SSL/TLS filtering for the dropbox, it connected successfully. In my case problem also appeared yesterday, 04.Dec.2020. I think something has changed with the last update of ESET Internet Security, which I have. B.t.w. on dropbox website they mention this problem with ESET SSL.
Problem with Dropbox and SSL/TLS protocol filtering
in ESET Internet Security & ESET Smart Security Premium & ESET Security Ultimate
Posted
I have the same issue. When I disabled SSL/TLS filtering for the dropbox, it connected successfully. In my case problem also appeared yesterday, 04.Dec.2020. I think something has changed with the last update of ESET Internet Security, which I have. B.t.w. on dropbox website they mention this problem with ESET SSL.