Jellyfin Chromecast message appearing on screen

[Efficient_Good_5784]

You could try following this guide I wrote: https://forum.jellyfin.org/t-guide-runni...er-compose

As for keeping your server, as long as you manage to copy/move the Jellyfin config folder to an accessible location, you can recreate it with any other Docker deployment.
I'm not familiar with how SynoCommunity handles Jellyfin, but if you can't find the config folder, I would ask on the them directly. They appear to have a Discord link on their main website page: https://synocommunity.com/