Problem of Proton Drive is not only in the missing linux client. There is no support of WebDAV that makes integration with many open source tools (like note taking apps or photo management tools) almost impossible. Nextcloud is much better for me. Without a WebDAV (or one of other popular APIs) it looks like an attempt to create “walled garden” with vendor-lock on Proton, imo.

What is wrong with an existing FreeCAD? It seemed to me that the project is very active

Org-mode + emacs. Org-roam + org-roam-ui to vizualize zettelkaster.

Wow! Looks exatly as what I need. And GPL license 🤩🤩🤩!

I’m using the managed solution from Hetzner (they name it “Storage Share” but it is just the same Nextcloud). Here you have the admin rights in your own instance, including setup keys, cryptography, access, etc. I’m paying 4.29 eur/month for 1Tb of storage (including all the services of Nextcloud, like tasks, contacts, etc.).

I think that maintaining the own Nextcloud on the EC2-like instances will be even more expensive and also requires a lot of time. So, for me managed solution with control over keys is a good balance of privacy and control over data versus number of efforts and technical complexity.