In the end, the main problem will be in the application.
I installed krecorder on Phosh and recorded the audio under the conditions described above:
Updated 2022-03-08:
Communication with SoundRecorder developers has indicated that the difference is due to the use of a different codec/format when saving the recording. So I switched from the original FLAC to Opus with this much better result - gnome-sound-recorder 75%.opus
