There is a lot here with varying degrees of helpfulness. I’ll add one thing. Many have commented essentially “build stuff”, and that is solid truth. That’s how you get better. But just like the whole perfect practice makes perfect, there is one fundamental detail that must be included. Build systems that you understand deeply. Not the code; that you are learning. But it is best to build things where you understand the outcome behavior of the system.

For example, if you don’t really understand what graphics rasterization is, building a raster program, even with a good guide, isn’t going to help as much as you might think. Though it will help you understand graphics, so go nuts. But if you really understand how baseball stats are calculated, do something with that. It will be much more gratifying and the code will be the part you’re learning, not the system it is implementing.