In reply to @tauruuuuuus "happy to help another": If you want to check out my
code it is here 😄  https://github.com/adokitkat/esp-idf_nim_template

It helps you build Nim program as a static library which is then linked to
ESP-IDF binary, i.e. you can write code in Nim and call it from ESP-IDF C code
easily.

I wrote it quite a time ago and now I just updated so it still works.