I’d also recommend this book that Seb is a coauthor on!
https://www.realtimerendering.com/
A production engine and/or renderer can be really overwhelming. I wouldn’t recommend that as the first place to look but it is a great resource that isn’t crazy hard to get into once you’ve learned the CG fundamentals if you focus on just the shaders. They are a far smaller amount of code, have far less interdependencies which make them easier to understand as stand alone snippets. Shaders are also becoming the primary location for graphics techniques. In the past huge amounts of the algorithms would be on the CPU but that has flipped. Mostly the CPU is used for setup and the bulk of graphics algorithms are in shaders now.
That said there is a great amount that can be learned when you are starting out by writing your own version of it, no matter the domain. Write your own hash tables, search algorithms, BVH building, mesh importers, parsers, shader parameter reflection, etc. Write even stuff that might not seem relevant in modern era like your own basic software rasterizer. Don’t reinvent the wheel unless you want to learn a lot about wheels which is exactly what you want to do early on.