I haven't migrated apps (except ditching Evernote), but I use Obsidian with obsidian-livesync and it works great - typing on my phone live updates the notes on my PC. Downside is you need the self hosted software running somewhere
I've been considering switching to Jellyfin for a while due to concerns about Plex either becoming worse or them peering into my library. Any idea how the apps work on Fire TV Stick? I have one for home and one I take away with me and it all works seamlessly with Plex
Maybe run through the installation again, and run via Docker if you aren't already. It was plug-and-play when I set it up
Alternatively, obsidian offers a 1st party paid sync feature