The way Proton works is really fascinating, and also requires a ton of effort from Valve. Recently found out most games are "unsupported" because they require proprietary Windows Media Foundation libraries that can't be redistributed on the Deck - so Valve actually modifies the source game assets to no longer depend on the proprietary libraries.
These games often run flawlessly with Proton GE, a community version which includes the proprietary libraries (but must be installed via Desktop mode, thankfully there is an app on the Discover store that does this automatically)
I'm glad to hear that the main author of Proton-GE is joining forces with the various non-Steam Linux game launchers to make game compatibility even more seamless for the wider Linux user base in general!