I personally use Mullvad and love it but it is not conducive to helping seed due to port forwarding being blocked.

Like another person said they resolved to that here: https://www.reddit.com/r/ProtonVPN/comments/8ww4h2/protonvpn_and_tesonet/

I guess you decide if you like the response or not but that was a long time ago as well. 🙂

I see. Somehow I missed your first edit with that information. It does not seem like that’s an option given the response on the GitHub discussions: https://github.com/bitfireAT/davx5-ose/discussions/318#discussioncomment-5814992

They suggest:

creating a Tasker automation, or use an specialized application for synchronization like Syncthing or FolderSync for example.

Apparently there’s also the option to use NextCloud and their app if you want to go that route like someone else suggested.

Yes I’ve been using DAVx⁵ for many years to sync my Synology Calendar to my phone via WebDAV and my contacts via CardDAV. Any concerns you have?