@jakob Hi, yes, it is probably related. I met this type of button on the Lenovo Yoga 370 (my full review and workaround: https://www.davidrevoy.com/article976/lenovo-yoga-370-on-gnu-linux-technical-companion-article ) It's still possible to inject something via xsetwacom. The syntax is a bit weird:

xsetwacom --set "$YogaEraser" Button 1 "key +ctrl button 1 key -ctrl" # color picker

(for a Ctrl color picker modifier) and an eraser icon still appears on Krita, but it pick colors. On the XpPen, this workaround even doesn't work.

@davidrevoy Yeah sadly the configuration options of most other tablet drivers on Linux are "meh" compared to the Wacom driver (and even that isn't perfect).
I would really like seeing the Wacom driver to be changed into something more generic so that xsetwacom (and GUI tools for it) work for all the other brands as well...