Ive experienced the same thing, but have attributed it to gaining more experience. I feel like the questions answered on stack overflow usually are ones that one can trivially solve by knowing where to find documentation, and the questions I end up wanting help with are too specific to bring up sensible search results. Maybe I'm just bad at using search engines though...
I think experience (learning where to search) is a part of it.
But a lot of the software I was working with 10 years ago was not open-source - these days I can look up the source all the way to OS level when doing Android stuff for eg.
And documentation is really just much much better - MSDN of old was considered gold standard but nowdays it would be considered bad documentation - like someone else said above docs moved from pure references to more use case focused which makes it much more searchable and eats in SO space.
This was my thought. When I google stuff and will still see stack overflow as a top result but click on the official documentation instead, which is usually the 3rd or 4th result. SO is still showing up, I just visit it less because I get more value from docs these days.
