If he's looking for something social.... Consider Brighter Shores.
It's a modern table top styled MMO by Andrew Gower (the RuneScape guy). Just like RuneScape it's a point and click adventure MMO so ... it's really easy to pick up. It also works great as a windowed game, has low hardware requirements, and everything is saved server side so progress is pretty much impossible to lose.
It's got 2 free episodes (which is a lot of stuff to potentially do) and the optional subscription is currently $5.99/mo so it's also very affordable.
Linux is not natively supported but it runs great under Proton ... and the team seems very keen on making it work on as many platforms as possible.