I would like to suggest R.E.P.O.. I'm not sure if it would be added, since it's not exactly a sandbox game and it's fine if it's not added, I'm putting it out there because I want to find other people who also play it.
There is however, a large modding community for it which includes cosmetics, custom maps, things that increase player lobby limits, adds more monsters/items, etc. There's also a pretty creative and large fanbase that creates all kinds of art of the game and it's characters.
So I think people would share things like updates, mods, and creative creations and I'd also hope there would be public lobby sharing as well.
