https://wccftech.com/steam-deck-steamos-3-2-refresh-rate/

A new Steam Deck SteamOS update has gone live today, introducing plenty of improvements to the handheld console by Valve.

Update 3.2 brings the option to adjust in-game screen refresh rate on the fly. The default value is set to 60hz, but it is possible to slide it down to 40hz.