I've often used it, but just checked and now it doesn't work.They have improved the UX, pray they do not improve it any further.
I don't want to have an account (because they want email), so it looks like this is the end of github for me.
EDIT: in android firefox, I found the "Request Desktop Site" works (on a code page) e.g. https://github.com/termux/termux-app There is also a desktop link in the footer, but it doesn't work.
WARNING: If I try the desktop link and then "Request Desktop Site", I get to https://github.com/site/mobile_preference (a 404). Starting fresh and just doing "Request Desktop Site" works.
I saw there's now an option in Github user settings which allows you to mark your entire account as always serving desktop pages when you're on mobile.
Ironically, can't dig up the link on mobile since I've not yet clicked that button.
"Mobile settings"
[ ] Opt out of mobile pages
This will cause all your sessions and devices to only experience the desktop site for all pages. Pages designed to be responsive will still scale down properly.