Here are some that our group has enjoyed:

Project Zomboid: amazingly vast and deep Zombie long-term survival isometric game. If you’re into this, you’ll play for hundreds of hours. The cost-playtime ratio is off the charts.

Heave Ho: super crude 2D graphics, but absolutely hilarious gameplay

The Ascent: beautiful cyberpunk-themed isometric shooter

Broforce: very entertaining pixel-art 2D platformer/shooter (think in the style of Contra, but funnier) - we played this through to the end, which is rare for us

Overcooked: very entertaining 3D co-op cooking isometric game (you’re running a restaurant kitchen)

Unrailed: similar to overcooked, but you’re keeping a train running instead of cooking

SWAT 4: old 3D FPS, but still good. I think this is only at GOG, not Steam

Honorable mention: Hidden in Plain Sight. While not a co-op game, it’s relatively friendly, funny, and not heavily slanted to make better players run away with it because it doesn’t rely heavily on reflexes and coordination. Check it out if you can. Works great for couch play too (everyone playing on the same computer/monitor).

Edit: all of these handle at least 4 players, which was a requirement for us. Some of them, like Zomboid and SWAT, can handle more than 4. I’m not sure how high the others can go.

Edit 2: check https://www.co-optimus.com/ too, if you’re not already familiar with it.