Computer Configuration > Administrative Templates > Microsoft Edge - Default Settings (users can override) > Games settings
Both
HKLM\Software\Policies\Microsoft\Edge\Recommended
OBSOLETE: This policy is obsolete and doesn't work after Microsoft Edge 140. Microsoft Edge Gamer Mode allows gamers to personalize their browser with gaming themes and gives them the option of enabling Efficiency Mode for PC gaming, the Gaming feed on new tabs, sidebar apps for gamers, and more. If you enable or don't configure this policy, users can opt into Gamer Mode. If you disable this policy, Gamer Mode is disabled. Note: Starting in Microsoft Edge version 141, this policy is obsolete because the Gamer Mode feature has been removed.