A pile of outlets have run a lot of benchmarks on the Steam Deck (we haven’t gotten one yet). However, one of the big question marks surrounding the Steam Deck’s gaming performance has been the effect, whether good or bad, of its choice of operating system.
See, despite being a gaming PC at its heart, the Steam Deck doesn’t ship with Windows.

Source: Hot Hardware – Windows Graphics Drivers For Steam Deck Are Out, Gamers Start Your Benchmarks