I emulate a lot of old games on my Steam Deck. It’s not too hard, but requires some work. I will do the work for non-Steam stores if/when there is something I want to play from one. However, I suspect not releasing your games on Steam will really limit your reach. My guess is that most people won’t go through the effort to get itch.io games work on thier Deck.

Hopefully Crunchyroll or someone buys RWBY and finishes the series