On Manjaro (which is based on Arch) I never had this issue, so that's why I'm guessing Ubuntu decided differently. 🤔

The issue was related to a pulse audio property. Had to put "flat-volume = no" in a config file. It's a feature for auto-leveling sounds based on the loudest application.
According to the arch wiki, this is the default (aka off), so I guess Ubuntu decide to enable it by default ?

The yearly blog post is late, it should have been published in November. Hopefully it will come out soon, proofreading is almost done and motivation is back. :)

No worries, I was happy to answer still. :)

This one is a Keychron V6 QMK. I also have a very similar one at home (Keychron Q6 QMK).

The result is nice to the ears, and also less of a pain to press !