Yeah... I hope the Nintendo Switch port is brought to Steam Deck too. I gave Factorio a quick go a few days ago and it was painful to play (at least with the default key config)
Regarding the ecosystem, the Steam Deck is a x86 PC. It comes with SteamOS, which is an open Arch Linux based distribution. You are free to install other operating systems like Windows on it. The out of the box Steam experience is quite good, with lots of games on the Verified list[0], and they play really well. People also install non-Steam games and software, including console emulators, and there are growing communities around that.
Elden Ring plays well. I don't plan on using my switch OLED until the next Zelda comes out.