Under Narrow by number of players there's a Shared/Split Screen Co-op option. Just looking at it, the ones I'm familiar with are all couch co-op type games.

Yeah, the section is there!

Alas the pickings are just pretty slim on PC. Overcooked, Railed, Plates Up... some others. It saddens me significantly how PC gaming has gotten more and more and more 1 player 1 computer.

I also would love to see more Remote Play Together games, where other players don't need the game to play. I'm not sure if this is just one shared screen (fine) or if potentially the game can stream different things to different players (effing radical). But adoption seems quite low.

My personal experience with Linux has been Ubuntu ~1 week -> Debian 2 days -> Arch 11 years now.

It will require some time learning and reading through the wiki. I would definitely recommend trying it in a vm first.