type MyEqual<T,U> =
  (<X>() => X extends T ? 0 : 1) extends
  (<X>() => X extends U ? 0 : 1) ? true : false
type GetRequired<T,U=Required<T>> = {
  [K in keyof T
    as K extends keyof U
      ? MyEqual<T[K],U[K]> extends true ? K : never
      : never
  ]: T[K]
}

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<GetRequired<{ foo: number; bar?: string }>, { foo: number }>>,
  Expect<Equal<GetRequired<{ foo: undefined; bar?: undefined }>, { foo: undefined }>>,
]