Bluetooth Volume Manager can react to Bluetooth devices connecting or disconnecting.
It allows Android to remember the volume levels of different Bluetooth devices.

Available features:
• Music call ringtone and notification volume adjustment.
• Sending out 'Play' or 'Next' media commands.
• Opening a specific app.
• Keeping the screen awake.
• Preventing the volume from being changed.
• Restoring previous volume levels after disconnect.

This app can't "boost" your volume or change the volume if you can't change it through your device's volume buttons manually.

Permissions explained:
• 'Internet' for bug reports.
• 'Bluetooth' to work with Bluetooth devices.
• 'Modify audio settings' to change volume.
• 'Boot completed' to restore volume levels after reboots.
• 'WAKE_LOCK' to fix a bug on Samsung devices and to keep the screen awake if necessary.
• 'SYSTEM_ALERT_WINDOW' to launch apps when a Bluetooth device connects (only on Android 10).