If you can get away with just a static config file then pick toml or whatever and live a happy life (less so with yaml because it has some traps like when type autodetection fails spectacularly, try "a: yes".

Sometimes you might have a legitimate reason to build complex systems out of configs (cloud formation templates, kubernetes, terraform). In that case you might need a bridle to enforce some structure, to keep common things common, and to ensure that variants (such as testing and staging environments) can be expressed in a robust way.