> Proton has mail, calendar, drive, docs, sheets and more coming

As of today, there is no official Proton Drive client for Linux that I'm aware of. There is unofficial support via Rclone, but it is still beta and I try to avoid mounting via Rclone anyway. I recall that it wasn't a really convincing experience when I tried it with OneDrive.

Proton Drive for Linux (and Drive SDK) are announced for this year. Unfortunately not more specifically than “this year”.