The first one would have deleted nothing as it needs to match the whole name. I recommend running find with an explicit -print before replacing it in place with -delete or -exec. It’s good to remember that find has a complex order dependent language with -or and -and, but not maybe the best idea to try to use those features.

Jellyfin was forked when emby went closed source, I don’t think it had anything much to do with any specific event at plex