Yes I think active HG users are on their own here. While a lot code examples pre 2016 are a useful learning tool, in their current state most are not functional without editing.
I imagine those still using HG have heavily modified their install and users like yourself have submitted very useful revisions that have gotten GPIO back working on the RPI 2 and 3 range of boards.
As we know GPIO on the RPI 4 works “out of the box” on HG as demonstrated by @enterprised so the RPI range of boards function with GPIO again.
It would be nice to hear some feedback from the more experienced HG users on where they are at with their current installs. Remember we were told back in 2017 that HG was a finished project. That statement could be interpreted in two ways.