I’m trying to press keys using ydotool, I looked up how to get keycodes and didn’t find any legends for them, just this github issue saying to look at /usr/include/linux/input-event-codes.h.
There is no /usr/include on NixOS.
Use nix-locate from the nix-index (or nix-index-database) package to identify what package has this file, then use that.