Property type check

Question

I would like to define type that would allow only to use object keys that extends certain type:

interface Foo {
    a: number
    b: string;    
}

const c: TKey<Foo, number> = "a" // ok
const c: TKey<Foo, number> = "b" // nok

I created TKey as such:

type TKey<T extends object, V> = T[keyof T] extends V ? keyof T : never;

however it seems it always unwinds to never - what I'm doing wrong?

playground

Thank you!