JFYI, qastools v1.3.0 has a fix. It does work now without any workarounds.
Unfortunately, the project QasTools seems to be paused. I have to search new ALSA-only (without pulse) mixer.
Gaƫl, thank you for investigating this! I will add a link to your comment here https://gitlab.com/sebholt/qastools/-/issues/2 to the QasTools repo