Xiaomi 12 has no voice function when playing Happy Mahjong because it doesn't have the microphone permission to authorize the game, or the handset mode is not turned on.
Occasionally, the default sound output device of the game is incompatible. You need to open the settings interface, and then adjust the "sound input terminal settings" at the bottom to "Bluetooth headset", so that the game can readjust the input device and adjust the connection between Bluetooth headset and mobile phone in a more compatible mode.