I separate games into two categories basically: Games I can play any time/in-between other games, and games I need to follow until the end or I forget everything and have to start over.
I only play 1 big game at a time if I can help it until I either finish it or lose interest. That said, I can play as many secondary games as I want like Binding of Isaac, UFO 50, Balatro, and whatever multiplayer game I’m into right now.
Especially as I got more busy IRL it became really annoying to play a bunch of big games at once. I ended up restarting Ori Will of the Wisps because I came back to it later and forgot where I was and what I was doing.
Games with lots of mods for sure. It may be a generic recommendation but Minecraft with mod packs and gorgeous shaders is an amazing experience for someone who never got around to trying them.
Also if he’s a souls-like fan, I highly recommend Elden Ring’s convergence mod and Dark Souls 3’s convergence mod (they’re by the same team). It adds like a hundred new spells, new weapons and equipment, overhaul of some mechanics like having actual classes with game-changing effects, completely overhauls areas with new geometry, adds new enemies and bosses, etc. It’s a very fun time.