A secret game mode was discovered in the released beta version of Android 12. One of the Reddit users found it in the settings of the Digital Wellbeing app. And where there should hardly be a game mode: in the “Do not disturb” modes schedule.
You can already enter the game mode itself. There is a counter of frames per second, buttons to take a screenshot or start recording a screen, and a number of other items. And it all works now.
Sources suggest that in the final version of Android 12, the game mode will be brought to another place in the list of smartphone settings.