Hello!
I have a pen & touch Intuos Wacom tablet since about two months, and it works great! I also use Arch Linux.
But since a week, I can't put a different brush on the eraser end of the stylus than on its pen end.
On other applications (Xournal and Gimp), everything works as it should. I've tried reinstalling Krita and resetting its configuration, but it didn't work.
Does any of you have an idea, please?

Hm, that works here as it should, which suggests that it is an issue on your system, especially if you have remove the kritarc config file. (Reinstalling krita seldom makes a difference.)