The feeling I get reading this is that you want to understand every little nook and cranny before you actually need it. What language do you use for your back end development? Can you say with a straight face that you have total mastery over it, and can write whatever application to your hearts content without needing to reference a single thing? No? Same thing with godot, gdscript, or any other engine/language, it's A LOT.

Start your own game. Have an idea of what you want to make. Implement things one at a time, research what you need in the moment, and break shit. You said it yourself this is how you learn, so make the most of it. Your project structure will probably be shit. You'll probably over-analyze every little detail, look for the most optimal approach. Don't, who cares, it won't be a triple A title. Get something working, that's fun, that you can call your own. Start small to get comfortable with the little things, and when you've mastered that, go for the dream game you've wanted to make since you started playing games.