After the latest hearing safety standards update, output limits have been added for both wired and Bluetooth earphones to protect your hearing. If you notice that the sound from wired and Bluetooth earphones is lower compared to previous devices, this is a normal phenomenon. Please rest assured.
If you are dissatisfied with the volume, you can go to [Settings] >> [Sound & vibration] >> [Sound effects] >> [Scene selection] to adjust the volume effect. You can also customize the audio output by going to [Sound effects] >> [Graphic equalizer].