It’s exactly the same steps for both Plex and Jellyfin. There’s just one additional field when you login, which is your server address. That’s it.

I’d say Jellyfin is even easier than Plex, because when you create an account it’s nice and clean, while Plex pushes you to see their own ad-riddled content. Cleaning up a new Plex profile takes time and it’s annoying.