Наш код

const users = [
  { id: '123', name: 'John' },
  { id: '345', name: 'Anna' },
  { id: '567', name: 'Kate' },
  { id: '789', name: 'Jane' }
]

function groupNameById(result, user) {
  return {
    ...result,
    [user.id]: user.name
  }
}

const groupedUsers = users.reduce(groupNameById, {})