create a typescript type that excludes everything but specific sub-type

picked.ts

interface SeatingGroup {
    id: string;
    name: string;
    freeSeats: number;
}

interface Customer {
    id: number;
    name: string;
    tag: string;
}

const PickedKeys = {
    id: 'id',
    name: 'name'
} as const;
type PickedKeys =  keyof typeof PickedKeys;
type Picked<T, K extends Extract<keyof T, string>> = Pick<T, K>;


type SeatingGroupItem = Picked<SeatingGroup, PickedKeys>;
type CustomerItem = Picked<Customer, PickedKeys>;

const a: SeatingGroupItem = { 
  id: '',
  name: ''
}

const b: CustomerItem = {
  id: 1,
  name: ''
}