I'd be curious to hear others chime in, but I feel like the situation is very similar to this article talking about games. Do you want to get pixels to the screen/file? Shaders and materials (authoring or implementing)? How commercial renderers are organized? My job is mostly using commercial tools, but a lot of us have made toy renderers, read books, and taken classes to reimplement the fundamentals.
It's been awhile, but a few common, imho approachable, sources are:
https://github.com/ssloy/tinyrenderer/wiki - a rasterizer that starts with drawing a line
https://raytracing.github.io/ - a basic raytracer that incrementally adds features
https://www.pbrt.org/ - I've heard good things from people who have gone through the whole book. I haven't taken the dive, but thumbed through it and jumped around.
I wouldn't dismiss realtime stuff, either. Often, the concepts are similar but the feedback loop is much faster. I liked the UE4 docs on shaders talking about pbrt and the simplifications they chose when implementing it. There's a bunch of resources out there. I don't think single source is comprehensive. I say, start with something simple and find resources on specific things you want to know more about.