There was a third-party one but thankfully Steam built one too, and it actually shows stuff that won't work on the Steam Deck at launch. So, here's what it gave me of my library. I was a Humble Choice user for months (and still have to redeem some stuff) + bundles over the years so I've got some stuff I don't normally play listed here.
( Verified, Playable, and Unsupported items )