Atari 2600 because it’s the one I got to play the most and having video games outside of the arcade was mind blowing.
I never had a Vetrex but I would see them and always wanted one. Still do lol.
Not a “console” per se… but in that time frame… Commodore vic 20 or 64 would probably have been my most played games.
Heroic launcher is pretty good alternative. It has a feature to “automatically add to steam” as well that should make a link in the big picture steam deck mode so you don’t have to drop to desktop mode to make them work as well.