Store configs in the program if you can. Store in INI, TOML, or something similarly simple for humans if you must. Never use anything that requires matching syntax as the default (closing tags and matched brackets being the two main ones).
JSON is already strictly worse than XML though as it doesn’t support comments and multi-line strings in a sane way.
Thanks, but I tend to ignore this. Every time you, as a direct end-user, provide feedback on format or software, someone appears with a whole philosophy around why you shouldn't be like that and what you should do instead. And sometimes there's no "why" part even.
But I really don't need philosophy. I know what I want, and I want json with $subj, //comments and optional key quoting. Feels like some people just love making inconvenient things standard and/or teaching others how to live. (I mean the idea "json is not for X" here, not your comment)
JSON is already strictly worse than XML though as it doesn’t support comments and multi-line strings in a sane way.