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.
Heck, I’d even take it a step further and have it include basic system specs for each review since Steam already gets that info.
That would get complex for games that are played for lengthy periods of time and across different builds. Basic specs as of the review would be cool though.