Does CasaOS has a way to mount local folders on containers? if that’s so, the only thing you should do is first, stop Overseerr, then install Seerr, point Seerr’s config folder to the same local folder as Overseerr, and run it. Seerr will migrate the configuration and everything will be as if you haven’t installed anything new, Seerr looks and behaves exactly as Overseerr. Then you can delete your Overseerr installation, but make sure that process doesn’t delete any local configuration.

I don’t think the problem with Jellyfin is Tizen’s framework, the client looks like a fair webapp, with nothing much changing from what the browser client is. Jellyfin needs some serious UX input, and could learn some stuff from the other video apps.

what’s really federation on a system that isolates conversations per server? can you reply to a message from one server on another? maybe the main thing would be single account, because even friend lists from multiple accounts could be merged

Debian on the servers, Diet-Pi on the SBC’s, all containerized.