My initial thought was something like Elder Scrolls or Fallout, but I think I would be happier in something with a robust building system. Minecraft would work but something like 7 Days to Die would work too and add a bit more challenge. Maybe Valheim, I haven't played a lot of that but the building system seemed good the little I played?
Edit: I think I would choose No Man's Sky, actually. Endless exploration and a semi decent building system.