Some folks have pointed out X-Com is a turn based game, and I agree with the suggestions that fit that.

On the off chance you actually want a real time game, I’m a huge fan of the Kingdom series. The co-op one is called Kingdom Two Crowns. It’s an interesting take on real time strategy as it’s a 2d side scrolling game. You are managing a growing colony in a hostile land, and you have to build up your economy enough to construct a boat and sail to a new island. You end up having to double back to earlier islands as you unlock new tech, sometimes finding your village chugging along nicely, sometimes finding quite a grim scene in need of cleaning up.

It’s a very chill game for the most part, with some higher stress moments that are paced well imo. I personally love the art style and music.