I'm quite a bit influenced by suckless tools. For example, I adopted
their system of using "config.h" files.

For some of my programs, this was a mistake. "config.h" is great for me
as a developer, but it really sucks a lot for normal users. Want to
change the font of your terminal? Go ahead, recompile the damn thing.

Some of my software uses GTK and GLib anyway and, guess what, GLib comes
with an INI parser:

https://developer.gnome.org/glib/2.68/glib-Key-value-file-parser.html

Why not just use that?

Most suckless tools have few external dependencies, meaning they have to
implement lots of stuff themselves. In that scenario, it really matters:
My window manager, for example, does not use GLib, so I would have to
implement some config file parser myself -- or link against some JSON
library or something. Both of these option are bad, IMHO. This is where
"config.h" really shines.

But my terminal does use GLib. I might switch to INI files here.