To be more specific, I changed to the mpw-one-b tag of the openlane checkout and now I'm failing to rebuild the pdk. Is there some step-by-step instructions or are we at the point where I should just clean out the world and rebuild everything?

Yes This should help https://www.udemy.com/course/vsd-a-complete-guide-to-install-openlane-and-sky130nm-pdk/