If you've read the TeXbook, you probably noticed that there are some outdated aspects of it. Most people don't use bitmap fonts or DVI anymore, they use opentype and PDF. Because of this, the engine evolved from TeX to pdfTeX, XeTeX and luaTeX. Two projects worth checking out if you are interested in a modern version of TeX, are:

OpTeX https://ctan.org/pkg/optex

Minim https://ctan.org/pkg/minim