Never in the history of Steam have games published on Steam been specifically marked and adapted for a single device. That will change this year as Valve launches a portable mini-PC called Steam Deck, for which they have devised a new game verification system called Deck Verified.
Checking the compatibility of games with Steam Deck will be done on four levels: according to the control system, screen, system support, and usability. It will be seen whether the game has support for the controller, whether it supports a minimum resolution of 1280 × 720, whether its anti-cheat solutions support Linux / Proton, whether the game has a launcher, or something that cannot be controlled by the controller, etc.
The games will also have four levels of compatibility: Verified, Playable, Unsupported, and Unknown. Verified is the level at which the game works ideally on Steam Deck. At the Playable level, the game can be played, but the player must adjust the controls or something, etc. Unsupported are games that are not supported, for example, VR titles. The unknown category belongs to games whose compatibility has not been tested yet.
This information will be seen on Steam wherever you use it. But if you use Steam on the Steam Deck, then the first tab of the Steam Store will only show games with full verification. It will be the so-called "Great on Deck" tab, while all other supported games will be highlighted in other categories.
Valve announces that they plan to test most of the games on Steam before the release of Steam Deck, which is a huge deal because Steam has over 50,000 titles. Testing will continue with future games coming out, but if Steam Deck proves successful then Valve will have less to do because the developers themselves will want to optimize their games for that device.