It's not that it has stopped, but there is less and less open topics where there is no solution. And those topics are usually (in my experience) niche topics and will get better discussion in GitHub issues or in a similar system. Or related to a legacy stuff, then SO could help.
In addition to that, quality of experience, code, as well as quality of documentation increased comparing to before .net core. I find myself often going to the official docs for documentation now, or just look in the sources or even debug the internals using available debug symbols.
