After the "media volume sync" is turned on, the connected bluetooth devices such as earphones and speakers will synchronize with the volume of the phone. When you adjust the volume to a suitable volume, you can turn off this function to avoid the bluetooth device from adjusting the volume too much.
Setting Path:
realme UI 6.0 & 5.0: Settings > Bluetooth > Click the connected Bluetooth device > turn on Device volume sync
realme UI 4.0 & 3.0: Settings > Bluetooth > three dots in the upper right corner > Advanced/More settings > turn on Media volume sync
realme UI 2.0: Settings > Bluetooth > Advanced settings > turn on Media volume sync
realme UI 1.0: Settings > Bluetooth > two dots in the upper right corner > Advanced settings > turn on Media volume sync
realme UI R & S & T & Go & U edition: not support
