How to chain async/await using for data that depends on the first call

Use an async function for your map function and then use Promise.all on that result.

async function getUsers() {
  const users = await Api.getAllUsers()

  return Promise.all(users.map(async (user) => {
    return {
      id: user.id,
      group: await Api.getGroupByUserId(user.id),
    }
  }))
}

When you map with an async function you essentially get an array of promises. That's why you need Promise.all