1. There are plenty of beginner tutorials. Often they just go through the examples from the docs or show a very simple proof of concept. Not very useful if you can read the docs.
2. Then you are left on your own reading through uncommented GitHub repos to understand how to put these things actually into production for use cases that go beyond 'add a todo to this list'.
You almost never find tutorials on how to structure your application, best practices, common mistakes etc.
That's the knowledge that is really helpful though and that I would pay $$$ to learn. Not 'how to create a simple todo app'. Why are there barely any learning resources that target the intermediate level?
More intermediate stuff goes into the data structures and algorithms. https://sp19.datastructur.es/ ^UCB's Josh Hug is a good lecturer, also provides course textbook, hw, side projects.
For best practices, try to get the Head First Design Patterns PDF.
Common mistakes? Search for "Effective Also, goalkicker.com has compiled a lot of intermediate stuff from scraping StackOverflow question-answers.
1. Out of the total time spent in building an application, a non-significant amount of time is spent on boring tasks to make the application real world ready. In some cases at least, you use third party libraries and custom developed components to do so. Including those in a learning resource/tutorial will, at least in some cases, make the code exponentially more complex to absorb.
2. Some of the code you use for building production-ready applications is proprietary - either proprietary to the developer or to the company.
Sidenote: I would argue that we have an abundance of resources. What we don't have is that many laser focused "here are the 35 most common gotchas you will face while moving this to production and here is exactly what you need to do" type of resources.
For exploring some huge codebase where there is no design documentation one way is just to use a fancy ide and sabotage something to see what it breaks in your ide, then you can trace what code is relying on. Some open source projects have books written about their architecture, you could also start with those then everything you see there is often similar in undocumented projects in my experience, in terms of organization of code like where is the directory containing all the core functionality, where are the feature addons.
As regards educational content, I'm at an early stage with this, but I've got a couple of videos over on YouTube https://www.youtube.com/channel/UC17mJJnvzAa_e9qQqLIfIeQ
As for your question as to why there are so few intermediate level learning resources, I think it's because the market size for intermediate stuff is much much smaller than it is for beginner resources and therefore content creators prefer to focus on the beginner stuff.
Maybe this is the result of commercialization of information: much finer optimization of follower count inevitably leads to oversimplification and overselling. And experts are increasingly less motivated to share knowledge with non-experts, like in academia where clarity of explanation to outsiders is sometimes valued negatively.
Also, most of the useful beginner to intermediate level content is created in video format, and that’s just grossly inefficient for a busy person: you cannot quickly scan a video, and you need sound, and good understanding of spoken English (IME much harder than reading) so the barrier to learning is actually higher.
Also, there were blogs, and now there are mostly walled gardens. In many industries (e.g. I’m familiar with professional dog training) most information is there and is poorly accessible.
I’d like to hear other opinions too.
Unfortunately, I can’t remember any source that is publishing such materials on regular basis, seems that this type of knowledge is tightly connected with exact company best practices and it takes a lot of work to make this knowledge useful for the general public.
You mention video walkthroughs and that you would pay for something like this. I'd love to do a video call and chat to learn more: nirmalthacker@gmail.com
The other aspect of advanced is how to maintain an application and write it so its easier to maintain. Once something is live, how you get changes in, fix bugs, monitor, etc. is not really talked about online because it is boring. It is a combo of process, tooling and some tech.
(Judging from your comment would I be correct in guessing that you are doing mainly JavaScript stuff? If you are, then the Python world is generally a lot nicer.)
-Just my thoughts.