Yes the documentation for Nginx at least VERY out of date indeed.
I have experience with Ubuntu and we have been using pagespeed in production with Nginx for a long time without issues and this includes Ubuntu v18.04+ & . The latest build ( 18.104.22.168
) isn't easy to compile because the libraries are in beta (although I do have some instructions if you want them). The Ubuntu 12+ instructions are still valid for Ubuntu 18+: https://www.modpagespeed.com/doc/build_ngx_pagespeed_from_source
I briefly checked the auto-installer and it looks like it should still work (for the earlier version). If not the manual install (compiling from source), is possible and stable. I always compile from source.