For config formats I'm finding HCL[1] to be nice for my use cases. It has comments, no requirement for double quoted identifiers, and is actually simple. The main issue was the only implementation is in Go, so I had to write a port to C++.
I've only got one FOSS project using HCL but I think of its' bundled HCL config file is an attractive part of its UX: https://github.com/LukeB42/psyrcd