This article is a nerd snipe. Be forewarned. I had some hallucinations of spending the next decades solving crossword puzzles as I read that, but they seem so arbitry I would go crazy, I'll stick to mathematics puzzles.
Where do you get your mathematics puzzles?
I basically picked a "side project" that I wouldn't mind doing forever.. So a hobby.. And then I just collect ideas that could be useful and I slowly get bored and go deeper until most of what I read and watch is more "advanced" than it was before... Maybe one day I'll be considered an expert problem solver, if so, it'll be because I took the time to try and solve one problem thoroughly and so many subproblems are cross-disciplinary. When you have some concept of "wasting time" then you'll have too much anxiety to follow this process in a way where you can develop a natural and relaxed approach to problem solving. If I'm wrong and that you need the anxiety to break through some ceiling then I'll spend my life as a happy layman.