I've been learning (mostly 2D) graphics as my side project for a couple years now. I spend a ton of time on this project. I still feel like a beginner. It is one of the more complex topics I've ever delved into.
I've crawled through more topics than I can list here. Many of them were not easy to learn, due to disorganized learning resources and materials.
Documentation and information is scattered, frequently outdated, sometimes sparse, and just downright messy. OpenGL and its many quirks and legacy versions muddy the waters too. I've considered trying to pull this into one big guide, hopefully resulting in something like the Filament docs [1].
Side note: macOS (my dev env) is a terrible place to write OpenGL, I've learned. Debugging tools are practically non-existent.