I ended up installing Syncthing using Termux following these instructions: https://www.stephenjianu.com/syncthing-android/

I like Amperfy and I think Navidrome has a Subsonic API: https://github.com/BLeeEZ/amperfy

I understand it can be annoying but when it does I temporarily host a text version of the article on my website and save it from there

Yes I use it and it works ok for me. Maybe Kobo will consider official support for Wallabag now that Pocket is discontinued.

I would recommend Wallabag or Readeck. You can use Koreader on your ereader for reading article saved with Wallabag.

I use markdown files + Nextcloud for synchronization. What I like about it is that I can use any markdown editor. Currently I use Nextcloup app on mobile and Pulsar or Nextcloud Web UI on desktop.