12.Why is the sound very quiet when connecting the player to the Apple Airpods or some Bluetooth headphone?

You can solve this following the below steps.

1. Update the firmware to latest version first:Click here

2. Go to System Settings -> About device

3. Tap on the 'Build number' for 7 times to enable the Developer options

4. Return to System Settings, enter Developer options and toggle on the ' Disable absolute volume' option