Unfortunately Dropbox recently dropped support for certain Linux file systems like XFS, BTRFS, etc.
Effectively Dropbox is no longer the universal solution guaranteed to work everywhere, which was the reason I chose them before. They deliberately killed off their unique selling point.
These days I run Nextcloud on iOS, Windows and Linux and it doesn't complain about ZFS.
That lost them a shit-ton of goodwill. Too little, too late.