Where do you find deep knowledge on specific topics?

Most tutorials on specific tech stacks or technologies only teach you how to perform specific tasks, and that’s it. They don’t teach you the core concepts, theory, or the philosophy behind the technology. I find this approach tedious and a waste of time.

I mostly do projects related to game dev in c++ c# and already know some of the important data structures and algorithms and can solve medium-level problems comfortably on LeetCode. I know people may suggest doing more side projects to get better, but I want a good resource that can teach me the philosophy, good practices, and explain why certain ideas fail, rather than relying on trial and error when the knowledge is already out there.