It seems at some point “recently” (i.e. between whenever I last logged in and now) the GitHub login integration became dependent on the Google Analytics script loading, when I have uBlock Origin on blocking GA then the GitHub button doesn’t appear in the login popup at all. Checking the console there’s no errors logged so I’m not sure why it’s not appearing.
Actually, it’s not GA that’s hiding the button. “Fanboy’s Social Blocking List” has a very broad
##.btn-social block which is being triggered by the GitHub login button (and it appears uBlock doesn’t log when it’s hidden an element on the page).
I’m not sure if it’s worth trying to change the button class just to workaround this blocking list.
It’s a general Discourse thing that applies to every other forum I’ve seen it on, too.
I added an exception rule in uBlock Origin for this.