That would only work for the contacts. And only on desktop. And I’m not sure if I trust it to work reliably. I might try it though.
I mentioned the problems with that here:
It uses rclone underneath, but, when I tried it, it seemed to be very slow. I think it may be because of this issue (I have 16 cores, so…).
rclone itself works, but it’s not the same as a sync client of course. Since I only backup to Proton Drive, it’s not an issue for me. But it’s still unfortunate.