That's really what the (Deck/Machine/SteamOS) Verified program is for. Valve tests games out on those platforms and reports results back for everyone on the store page. Publishers have the control to explicitly mark it as unsupported too.
Lepton may most directly target Quest games, but it's not like it wouldn't also enable flatscreen titles running on AOSP, and it's not like Proton is limited to the use cases Valve intended either.