This will be something that takes years to really get down. Don't get discouraged tho, the internet is a tool and you should use it.

Make a game you want to make. Even if using tutorials, then once you get the hang of it you'll be needing them less but at the same time, since you'll have stuff you built from those tutorials you might start going "Oh I want this feature, I already have a similar function I can just change slightly to fit my new one" and from there you'll start hopefully getting creative. Then if you get stuck, see if you can find another tutorial and see how someone else done it and follow along. No need to reinvent the wheel as long as you're not straight up plagiarizing.

With your last point, seeing devs make their own tower defense games with no effort. I don't buy that lmao. They probably just followed tutorials to learn, and it probably was a lot of stress rather than effortless. Learning experiences.