> If I install TeX on my Linux machine now, is that still compiled from the original Pascal source?
If you install TeX via the usual ways–TeX Live and MikTeX are the most common—then the build step runs a program (like web2c) to convert the Pascal source (with changes) to C, then uses a C compiler. (So the Pascal source is still used, but the Pascal "compiler" is a specialized Pascal-to-C translator.) But there is also TeX-FPC (https://ctan.org/pkg/tex-fpc), a small set of change (patch) files to make TeX compilable with the Free Pascal compiler (https://gitlab.com/freepascal.org/fpc/).
If you install TeX via the usual ways–TeX Live and MikTeX are the most common—then the build step runs a program (like web2c) to convert the Pascal source (with changes) to C, then uses a C compiler. (So the Pascal source is still used, but the Pascal "compiler" is a specialized Pascal-to-C translator.) But there is also TeX-FPC (https://ctan.org/pkg/tex-fpc), a small set of change (patch) files to make TeX compilable with the Free Pascal compiler (https://gitlab.com/freepascal.org/fpc/).
For more details see https://tex.stackexchange.com/questions/111332/how-to-compil...