The difference is not huge. The big one is that, to be "Verified", there are some usability criteria that need to be met (the game's text needs to be legible on

The difference is not huge. The big one is that, to be "Verified", there are some usability criteria that need to be met (the game's text needs to be legible on the Steam Deck screen, you need to be able to launch the game without any hacky tweaks like clicking around in a launcher using the touch-screen or something, the game needs to basically work out-of-the-box with the Steam Deck's sticks and buttons, etc) and if those aren't met then they will provide a 'blurb' which explains which ones are missing. Other than that, I have found that lots of games which aren't "Verified" play perfectly, and some games which are "Verified" don't launch at all (because Valve said 'hey! it works!', gave it the Verified badge, and then a month later the developers pushed out an update for the game which broke something for Steam Deck users).