Upgrading Jellyfin to Version 12.0: Migration Guide

Jellyfin 12.0 changes how major updates are numbered, moving away from the old 10.x.y scheme used since 2018. Previously, massive under-the-hood overhauls, like rewriting the entire database structure were bundled into point releases like 10.11. Because the version number barely changed, many installations treated it like a routine minor patch, upgraded without backing up, and ran into trouble… Source