Arotogo said:

I've tried three, but they only work with the app open in the foreground.
Perhaps it is that the application is not configured correctly.

That means if you run such an app in foreground you can make a phone call via Bluetooth and your conversation partner can understand you?

TorstenH said:

That means if you run such an app in foreground you can make a phone call via Bluetooth and your conversation partner can understand you?

Don't know.
When using apps with this feature, what you were doing was recording in the same app that was boosting the microphone. In the recordings, the reception of the microphone did improve.
I never made a call, since it did not seem safe to call or answer a call with the car moving and pending the application.

Arotogo said:

Don't know.
When using apps with this feature, what you were doing was recording in the same app that was boosting the microphone. In the recordings, the reception of the microphone did improve.
I never made a call, since it did not seem safe to call or answer a call with the car moving and pending the application.

Just for testing purposes you could try with this app:

Microphone Amplifier APK for Android Download

Microphone Amplifier 1.6.4 APK download for Android. Discover the small voice around you and high quality wav format recording.

m.apkpure.com

Arotogo said:

Don't know.
When using apps with this feature, what you were doing was recording in the same app that was boosting the microphone. In the recordings, the reception of the microphone did improve.
I never made a call, since it did not seem safe to call or answer a call with the car moving and pending the application.

What's behind System Settings and Performance Utils?
Maybe you've just overseen the relevant setting...

Arotogo said:

Don't know.
When using apps with this feature, what you were doing was recording in the same app that was boosting the microphone. In the recordings, the reception of the microphone did improve.
I never made a call, since it did not seem safe to call or answer a call with the car moving and pending the application.

Which options are available here and in the other menus?