Mining Mechs is a straightforward mine-sell-upgrade game by a single indie dev, and it's great simple fun. You dig down, mine ores, collect dirt, then return to the surface to sell them. That's pretty much it and it does get repetitive, but for €3 you really can't complain. Everything works, there's some dialogue, and a loose main quest that basically says "dig down another 100 metres" until you hit the bottom. Works great on the Steam deck, and there's lots of different mechs to play with.