SO used to have really god content for really some fundamental questions which gave it some credibility. As it accumulates more content the quality is really going down - I actively avoid SO unless I can't find any other source.
GitHub - literally every problem I have nowdays I spend searching through GH issues, reading through the code upstream and reporting back. For example I was working with .NET framework for a while (~5-6 years back now) and when dealing with closed source frameworks SO was a replacement for support channels. Now even as I'm coming back to a .NET core project - everything is OSS and on GitHub.
Docs also got better, MDN is now defunded by mozilla but where I had to do a SO search for random JS behavior I can now look up decent references on MDN. I think Google got better at indexing documentation as well.