Diablo 4

Has nobody mentioned Barotrauma? Had a few hundred hours of fun with this, my buddy and I. Especially if you don't mind shit being not very shiny. It is unique, and it keeps on giving.

Core Keeper comes out of Early Access soon I think and should be up your alley

You should try a wholesome cute game called Bread and Fred!!! It's got penguins!

Here's a co-op indie game I made for Windows PCs. $1.

https://www.cheerandtrack.com

Outriders. And a bit more tame but Unravel 2 for in-person.

Wildermyth is an awesome indie RPG that I've had a lot of fun with as a two-player coop game. It's a turn-based dungeon crawler with a strong focus on role play and party dynamics.

I hear great praise for Across the Obelisk as a coop game from my friends, although I personally bounced off of it. It's a roguelite deck builder like Slay the Spire, but with multi-player, lots of meta progression, and a heftier time commitment for each run.

Gunfire Reborn is a roguelite looter shooter that's a blast in coop. I think it's still in Early Access, but what's already there is enough for me to be happy with it as a full game. To me it's a spiritual successor to Borderlands in combat and gamefeel, but without the grinding.

Remnant 2 is sweet!

Super Mario 3 is pretty sweet

There's a game on Kickstarter called Outbound. It's in alpha access right now.

The game looks like it's literally Raft in a camper van. Haven't tried it yet but I plan to.

Steam link