JSMin is not the right tool for this. I'm sure it conforms to the JavaScript (ECMAScript) spec but probably not the JSON spec. Here's a trivial JavaScript function to convert JSON5 to regular JSON with no comments and quoted identifiers and all that good stuff:

function JSON5_to_JSON(str) { return JSON5.parse(str).stringify(); }

This is exactly what is suggested in the Usage section of the linked article.