Terraria might scratch your itch. It's a sort of 2D Minecraft that's a little less open ended. It's more RPG-like in the that there's a focus on getting better gear and fighting tougher bosses, but you can also build some crazy stuff if you work at it or get into modding it. it's not as easy to mod as Minecraft from what I know, however.

It supports co-op just fine, one of you hosts the game and the other connects, no need for external servers or anything.

It also has the benefit of being very cheap, often on sale, and still getting updates despite being out for eight years now.

Any of the Civilization games could do the same. 4, 5, and 6 are all on steam and do multiplayer. It'd be easy enough to hop onto an ongoing game to play a few turns. Being turn-based means it's definitely not fast-paced and stressful...though Montezuma declaring war on you because he's Montezumaand that's what he does might get old.