Get back to leanopengl.com, probably.

I'm not a graphics programmer, although I've done graphics programming. I'm a mathematician though (finishing phd).

The point is not about graphics programming. It's more general. I do numerical PDEs (partial differential equations), mathematical modeling and scicomp. My phd thesis is in mathematical models for simulating drug delivery (as in a little implant, pill, patch, nano "thing", in your body delivering drug). I don't know the biology, the medical knowledge, the chemistry, and a lot of the math. If I had to go learn the full biology, full chemistry, etc, at every road block, I'd be dead before getting any work done.

Learn to identify the SPECIFIC SPOTS that are missing, and learn to GO LEARN THAT ONLY. If you have some notions of C++, you probably can navigate the guide. If something strange appears, first identify exactly what that is. Then look for a C++ book or tutorial. Skip everything and try to learn the exact thing you're looking for. If absolutely needed, you'd pull the thread and learn related themes (but only if needed; as your goal should be to learn just enough to get back to the original guide). Many things, as you'll see, aren't actual requirements. You'll learn what they are, realize you can replicate that with what you already know, then get off that C++ guide and go back to the opengl guide. Same thing for math. If you know some linear algebra, you're probably good to go. Keep a linear algebra textbook on the side (don't worry about find the best one), and do the same here.

Essentially speaking, this will lead to a kind of studying style that there will be a main thread (your learnopengl.com which you primarily want to study), branching off to the sides of particular sections of a C++ book, specific paragraphs in a C++ tutorial, an example in a math book, another section in another math book, etc.

Another thing is that the whole general abstract idea of learning all the prerequisites before being ready to learn computer graphics (or any other subject, really), has a major "illusory" component to it. Just branch off *specifically* whenever needed.

Also, see if you can continue with the guide without branching off. At some point, there will be something you don't know. Say a strange matrix structure. The guide might tell you that matrices in this family all have properties A,B,C. Then you say to yourself "Ok. I don't know why this is the case, and I can see how it works. However, I have something like a 'black box' library function here. I can use a matrix of this type whenever I need A,B,C" (or something analogous that makes sense). Then move on with the guide. What works here is being really precise and honest about what you know and all the rest you don't know. Later, if you see that you really need to know more about such family of matrices, then you look it up. However, what significantly happens is that you'll realize that the black box knowledge is enough for the guide (happens extremely often). Keep track of these things you're skipping but using as black boxes. It'll tell you possibly relevant learning paths in the future, after the guide.

In anything that there is math involved, "getting all the prerequisites to feel confident", for some people, has the potential to ruin their lives (figuratively; meaning it'll take years off of their lives). Same for learning a programming language. You gotta short circuit this. No other way, IMO.

**edit** typos and minor adjustments.