Currently the /proc/self/mountinfo parsing code inside pym/portage/util/writeable_check.py raises an IndexError on WSL, as reported here: https://github.com/gentoo/portage/pull/49
In the master branch now: https://gitweb.gentoo.org/proj/portage.git/commit/?id=2593cb2c5d56e373c6c6e4f4663f25241e0e79b7 https://gitweb.gentoo.org/proj/portage.git/commit/?id=a000c492b9f12a43b75c2613323e29a472732259 https://gitweb.gentoo.org/proj/portage.git/commit/?id=9b31cd9f2823d742ce3431e480561244f00f1744
Fixed in portage-2.3.3.