FaceTime sound volume too low

Comparing calls between apps on MacOS, the sound volume on FaceTime is consistently too low and needs to be manually adjusted using the control panel or icon on the upper bar.

And back to normal volume when the conversation ends.

Using Skype, Zoom, MS Teams, there is no such problem: a conversation does not require any manual adjustment of the sound volume.

Is there a hidden preference in FaceTime to avoid these annoying adjustments ?