Sadly they explicitly don't support that. :(
> Now that there is a Steam Deck Native build, is Baldur’s Gate 3 supported on Linux?
> Larian does not provide support for the Linux platform. The Steam Deck Native build is only supported on Steam Deck.
> Now that there is a Steam Deck Native build, is Baldur’s Gate 3 supported on Linux?
> Larian does not provide support for the Linux platform. The Steam Deck Native build is only supported on Steam Deck.
BG3 already ran well enough on Linux, so I imagine this will only make it run better, official support or not.