“Linux + SteamOS” compatibility is a bit legacy. It mostly refers to games that have a native linux client (I believe some of the early Proton Validated games are included as well.
The Steamdeck (and generally speaking, any linux system) uses Proton as a compatibility layer with windows, and the “Steamdeck Verified” system is more relevant today. That said, even the Steamdeck verified system isn’t perfect. There are a number of titles that, while verified, have some problems with the deck, typically later in the game or after running for some number of hours. There’s also a vast number of games that while not “Steamdeck Verified” work perfectly on the deck and linux via proton (though you do have to enable it in the settings).
Always hide them? I don’t think so, but you could just browse https://store.steampowered.com/linux ?
Though it may include officially supported proton games? Not sure, tbh.