It was mentioned in the LTT coverage. Aside from native ARM games they have a translation layer(FEX) to play x86 games on ARM. They'll have a "Verified" tag like the Steam Deck for compatibility. I assume you'll still be able to force trying to run unverified games.

Edit: FEX is not a Valve thing, but an existing open source x86/x86_64 emulator that Valve is using. It's not clear if they're forking it or directly contributing though.