If you're interested in understanding the graphics algorithms and implementing them yourself, as opposed to using an engine or a library, check out https://gabr

If you're interested in understanding the graphics algorithms and implementing them yourself, as opposed to using an engine or a library, check out https://gabrielgambetta.com/computer-graphics-from-scratch https://gabrielgambetta.com/computer-graphics-from-scratch It guides you through writing a software rasterizer and a raytracer, and most of what you learn can be applied to GPU programming.