This is the equivalent of Sony requiring PSN account in countries where no PSN account exist. Just on a different technical level, but with the same outcome. This should be illegal.
I'm surprised Valve hasn't pushed a condition about this in their contracts stating that they can get a Verified badge only if they agree to keep the Steamdeck as a supported platform.
That or adding to all the games from the same publisher that are verified a badge meaning “has intentionally made become games unsupported in the past”