Extracting types of properties of generic interfaces still requires unnecessary generic type

When I have an interface with a generic as such:

   interface I1<S> {
      a: string;
      b: genericType<S>
}

and try to extract type of property a using I1['a'], typescript throws the following error:

TS2314: Generic type 'I1<S>' requires 1 type argument(s).

Should this not be fine since the extracted property type is not actually dependent on <S>? Either I am failing to understand how Typescript actually works or this should indeed be okay.

Playground Link

Property a type is not reliant on S, but you cannot omit the type parameter as part of the lookup. Some options:

1.) Set S to unknown

type T1 = I1<unknown>["a"] // string

2.) Declare a default for S in the interface

interface I2<S = unknown> {
  a: string;
  b: S
}

type T2 = I2["a"] // string

3.) Keep it generic

type T3<S> = I1<S>["a"]  // T3<S> = string
// doesn't make too much sense in this particular case

Here is a sample

It should be:

interface I1<S> {
      a: string;
      b: S;
}

and you need to give the type of S when making the object:

notice I gave string type for the S generic type parameter below, but this can be any type you want the "b" to be.

const i1object: I1<string> = { a: "a", b: "b" };
const i1object2: I1<number> = { a: "a", b: 5 };