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.
Games have specs on steam. We could easily get a performance percentage for gamers with less than optimal setups without blasting their systems. I personally have a good one yet may struggle during forced windows updates or when my ssd is getting heavy loads from my other apps. That would not be caught by such ratings.