This one went by quietly for whatever reason. Possibly because Halo stole the show entirely.
https://news.xbox.com/en-us/2021/12/01/coming-soon-xbox-game-pass-december-2021/

This one’s better than just Halo though. I just tried Generation Zero, (I’ll make a separate post) and actually really liked it. It has great coop potential for sure. Edit: oddly, I can’t see it anywhere in the marketing, but it’s been added. It’s the avalanche one that sets you in 80s Sweden, finding yourself battling a mysterious robot invasion. Up to 4 players.
ANVIL is the other one. I’ve had my eye on this for a few weeks. It’s early access but from what I’ve read, think Destiny if it was a coop Diablo-like. I’m downloading just now. Complete surprise that it’s on GP, I was going to buy into early access anyway.