Maybe just try the buttons offered in present Krita. I setup a kb shortcut to a ten brush spot for my favorite true eraser, then I just clicked the buttons at the bottom of the brush editor to be able to toggle my current brush into eraser mode.
then set my kb shortcut to toggle that mode. The reason for that awkward looking shortcut, that is the “)” on my portable keypad. The script was deleted from my resources a long time ago, but for some reason Krita keeps the remnants in my kb shortcuts. I had to go from W11 to Linux to get rid of the Kanvas Buddy stuff.
