. . . what do you use instead? AlternativeTo mentions (among a few others) Cozy and Filen; anyone use either of these? Internxt got a pretty bad review from someone on Medium.
I use whatever online storage service I want because you can add your own encryption layer so you only sync encrypted files. rclone supports lots of services and will also encrypt files for you.
This. It’s not as simple to get it working as it is on non-free OS’s, but with rclone I can get on Linux pretty much the same functionality I get from (eg.) Google Drive on Windows, including have most of the drive with on-demand access (meaning files are not stored locally, but downloaded / uploaded as needed) with a few specific folders synced for offline use. Since it supports a lot of storage services, I suppose it shouldn’t be that different to set it up the same way with Proton Drive.