If the majority of a users playtime at the time of review was from playing on Deck, the review will have a Deck icon next to it.
The game in the screenshot is SAND LAND. You can view the reviews here to easily see some examples of this new icon.
Unfortunately there doesn’t seem to be a way to filter reviews to show Deck reviews only.
I agree good. Idea. its like when people watch a movie on their iphone and then say it wasnt that good. You’ll enjoy a game more on a big screen running high fps