Code by Charles Petzold [1] is a fantastic introduction. It isn't so much the nitty gritty "this opcode performs this operation, and these are all the tricks to making it do things, edge cases and things you should worry about" and more along the lines of "what opcodes should a CPU have, and how do those translate into electricity flowing through physical wires?" I feel like really thinking through that book made MIPS and x86 assembly much easier for me.
edit: apparently a thing -- https://single-spa.js.org/