If you really want to be proficient in a certain domain you need to invest time doing things in that domain; getting your hands dirty. You can read everything about the subject but if you don't have practical experience you will not have a deep understanding.
You will not hit walls that practice will ultimately lead you to. Hitting walls is what makes you understand. It forces you to update your priors. To update the mental model you had of the inner workings.
The most important thing practice gives you is a roadmap to navigate the vast amount of knowledge of a domain. That roadmap is unique for every person. That is the reason why tutorials don't give you deep understanding; they are a transcription of the unique roadmap of the author. Because the author has another mental model he chooses certain steps that seem logical to him but not to you. Other things that are self-explanatory to the author are not to you.
Where do you start your practical journey? Begin small. State a problem you want to solve and find the most simple way to solve it. This is your starting point. Then, challenge your assumptions about the solution you have. Try to prove yourself wrong and build a solid mental model.
If you are comfortable navigating your way in that tiny realm, expand it. Like the blast radius of an explosion your knowledge will expand in concentric circles, touching other explosions of knowledge resembling a carpet bombing of expertise.
How do you know you are ready to expand? Again, this is highly personal. Some people accept higher levels of abstraction than others, but in general you should go to the level of abstraction that explains most questions you have of that tiny slice you are trying to understand.
If you are a curious person, and you should be if your goal is to have expertise knowledge, you will add more and more functionality. You will crave for things you do not understand and try to conquer them. Some subjects will not be interesting enough for you to explore deeper and you will settle with the level of comprehension you have of that subject. And that's fine. Other subjects, on the other hand, will capture your interest and have a huge blast radius, making you an expert of that.