Utility Typescript Type to know when exactOptionalPropertyTypes is set

isExactOptional.ts

type _Intersect = {a?:number} & {a:number|undefined};

//state of exactOptionalPropertyTypes
type IsExactOptional = _Intersect["a"] extends Exclude<_Intersect["a"], undefined> ? true : false;

Doesnt work past Typescript 4.6, but is easily replaced by

type IsExactOptional = {foo: undefined} extends {foo?:number} : false : true;