You can do it like this:

  type RequiredKeys<O, K extends keyof O> = Omit<O, K> & Required<Pick<O, K>>
  type Person = {
    name?: string
    age?: number
  }
  type RequiredName = RequiredKeys<Person, 'name'>

The opposite (making some of the fields optional, without affecting the rest) would be written like this:

  type OptionalKeys<O, K extends keyof O> = Omit<O, K> & Partial<Pick<O, K>>