> Surely there exist communities today for LaTeX that have been around since before SO began its life.

Yup, TeXhax has been around since 1986 [0], and comp.text.tex has been around since 1983/1990 [1], and both are still somewhat active.

[0]: https://www.ctan.org/pkg/texhax

[1]: https://tug.org/TUGboat/tb45-3/tb141lucas-usenet.pdf