Jellyfin Media Player is the main desktop app, but if I were you I’d probably set it up with LibreElec and use the Jellyfin Kodi plugin, since you’re looking for sort of a console-ized setup for your non-techie friend.
Now all that said, the Roku app is great and you could definitely just get your friend a Roku Streaming Stick+ and set up the JF app on it for them.