Alain, you might try booting w Solus OS. All the other OS you mention are all desktop derivatives of Ubuntu in one manner or another. Solus is built from the ground up, but shares a desktop environment with Ubuntu Budgie. Maybe it would have different audio solutions?
A reason for sticking with an Ubuntu derivative would be the larger repository of program choices, and your familiarity with apt vs eopkg.
If you are thinking it’s a kernel issue, you could try booting with 18.04:
Before you do (it does sound like you have exhausted a lot of options) check with David: how is the kernel different in 18.04.4? I know for a fact the kernel is older in elementary OS 5.1.4 than in the new Ubuntu Budgie 20.04.