Very different 'skill' levels, imho. Astroneer is a game that got 3/4 finished, something happened to the lead guy, and it's kinda in stasis since then. It's definitely G rated, and has some basic environmental dangers but that's about it. It's designed to play with your kids. I don't hold much hope for major updates for this game.

Valheim is much more of an effort. Theoretically, Valheim has a ton of potential (long list of things to get to 1.0). The world is much, much more dangerous. Progression is key, and building is custom.. but frankly kinda limited (and fairly idiosyncratic). It's designed to be solo or with your friends. It can be played casually, but generally it tends toward "serious" gamer. I do think they'll be making updates for a while, but it's not gonna be anytime soon. Previous updates have taken ages...