On Steamdeck, I haven’t tried multiple controllers, but with one, it has been rather seamless for both the PS5 and the Stadia controller. They are both Bluetooth, and when I turn them on they just work. That said, the original SteamDeck(which is what I have) doesn’t support CEC or Bluetooth waking, so the Switch wins out on automatically turning on and switching my TV’s input. The OLED SteamDeck is supposed to fix that, but I’m not paying for a replacement until this one dies or a SteamDeck 2 comes along.