Your own computer/NAS with tailscale for day to day usage of accessing your files from any computer from any other computer. Immich to replace the camera upload feature.

Taildrop needs improvement with files over a gig and between other users though.

Not free but https://tresorit.com is great. E2E encryption and has a Linux client too.

The main downside of Tresorit is that it does not support syncing symlinks. It also does not have LAN sync like Dropbox does. Tresorit does have E2E encryption, which is great. Only the enterprise version of Dropbox has E2E encryption.

That is unfortunate for both symlinks and for a lack of LAN sync. Not having the ability to deal with anything I throw at it does add risk that the sync isn't true, but outside of the OS I don't use symlinks. LAN sync would save data transfers over slower links but with E2E is this isn't too surprising that it's centralised.

Thanks for sharing, I didn't find this option when I looked. This might be a winner for my uses.

Google Drive with Insync client (paid), I’m using it with no issues for years on Linux.

I'm actively looking. NextCloud is on my list of maybes, as is S3 or S3-compatible services like OVH. I'm using Fastmail files as a stopgap via WebDav, but it's slow, doesn't give offline files, and I'll need to rig my own backup solution.

Everything I've looked at lacks a native client for at least one of my devices or has privacy concerns. Proton would be my first choice if they offered a Linux client.

The other route I need to explore is rclone - it claims to connect to everything. It would need to poll / cronjob to update rather than instant updates like the mainstream options. The downside is uncertainty - if Proton or whatever changes their private API or encryption scheme then things will cease to sync.

I haven't used it personally but I read about it before I decided to DIY, but MEGA has Linux client.

Syncthing! Syncs directly between devices. I also use a server, but could probably do without.