Notification sound volume is too high on my MacBook Air (MacOS Big Sur)

I am running macOS Big Sur on MacBook Air M1.

Notification sound volume for system notifications is too high on device.

For example, I am listening to songs playing in Apple Music on my MacBook Air using a bluetooth speaker. I get a notification. The notification makes a sound in the bluetooth speaker. The volume of the notification is too high. Much higher than the volume of the song. Also, the volume of the notification is independent of the MacBook Air volume level.

Because I could not bear the notification volume level, I turned off sound notifications for all of my applications in the Notification panel in System Preferences. However, there are system notifications for which I cannot turn off sound. One of these system notifications is the one when my computer connects to the bluetooth device or disconnects from the bluetooth device. Each time, it makes a loud bang and that loud bang is heard from the bluetooth device.

Is there a way to turn off sound for ALL system notifications? I went to the "Sound" panel in System Preference and set the Alert volume to zero. However, the loud bang is still heard when my computer connects to or disconnects from the bluetooth device.

Any suggestions? Thank you.