Helldivers 2 is an awesome game for this as it’s very cooperative and is also a shooter. Though you do need either a pc or a ps5 for it so I’m not sure if you can play it.

I’m a huge fan of Borderlands so would recommend that and I’m also a huge fan of Halo, the Master Cheif Collection is an absolute bargain considering what you get. Your brother with the Xbox will need to get Game Pass of some sort to join in for any games that are not free to play. Halo Infinite is free to play and has a PvE game mode, if that tickles your fancy.

Palworld is another kind of game playable multiplayer on xbox/pc.

Another vote for deep Rock galactic.

The Borderlands series might work. Also I believe L4D2 might run on all those, if y’all wanna coop some zombies?

Here’s a full list of crossplay Xbox and PC games. I figure if it’s on the pc, there’s a good chance it could be played on the steam deck as well.

Notable mentions in there that I’ve played and enjoyed are Destiny 2, Overwatch 2, Remnant 2, Left4Dead 2, (I’m seeing a pattern here), and Deep Rock Galactic.

If you want to play against each other, there’s always fighting games, if you’re into that. I’d recommend Guilty Gear Strive, Street Fighter 6, and Tekken 8, which are the most popular fighting games right now. There’s also Mortal Kombat 1 but I haven’t played it, so I can’t comment on it.

Enshrouded, Chained Together, Payday 3, Risk of Rain 2, Helldivers 2

The Quake games (1 and 2) got updated with co-op support and cross play.

Gangbeasts!

Every year I enjoy the hell out of Left 4 Dead 2 around Halloween. If you guys have never played it, oh you’re in for a fun time. Super cheap and runs on a potato at this point if your Xbox brother can find a computer.

Civ 5 was great for this. Me and another old fart in our 40s played it against each other.

Apparently I was the only one to read the title that way, but I thought your brothers died (late) in their 40s.

Portal 2 is only two player, but it’s my favorite game and it has a co-op mode with puzzles that require both people.

You will need games that have crossplay between PC and Xbox One so you can play together across different platforms. Multiple people have suggested Left 4 Dead 2, but that doesn’t have crossplay. Most of the shooters I personally play don’t have it, but there definitely are shooters with crossplay.

Here are my recommendations that have crossplay:

• Borderlands 3 — Collect wacky guns, travel the universe, and shoot bad guys together. The previous games in the series don’t have crossplay.

…Yeah, that’s it for crossplay shooters I recommend. For crossplay games that aren’t shooters:

• Overcooked! All You Can Eat — Chaotic co-op cooking. Work together to prepare, cook, and serve food in increasingly absurd scenarios: in the middle of the highway, on an iceberg, in a hot air balloon that crashes into a different restaurant.
• Ultimate Chicken Horse — Platformer where you build the levels together and then race to the finish. You only score if someone died, so you need to make the level extra dangerous.
• Moving Out 2 — Goofy co-op game where your group plays as a ridiculously reckless moving company. Carry furniture from the house and shove or throw it into the truck. No one will notice if you break all the windows.

If everyone is on PC, things will open up a good bunch. Old-school networked games generally still work. You can go FFA deathmatch in your old favourites or in newer arena shooters, like Warsow or Disco Dodgeball.