You can use .flatMap() to map your outer arr of object. For each inner nested object, you can filter it to only keep objects matching the id of 1 (as you've done). You can then use .flatMap() on the filtered inner array to map each role to its re-keyed object with label and name. The .flatMap() methods then merge the returned array results into one resulting array:

const arr = [ { users: [ { id: 1, login: "alex", roles: [ { id: 0, name: "admin" }, { id: 1, name: "moderator" } ] }, { id: 2, login: "bob", roles: [{ id: 0, name: "viewer" }] } ] } ];
const options = arr.flatMap(({users}) => users
  .filter(({ id }) => id === 1)
  .flatMap(({roles}) => roles.map(({ id, name }) => ({ label: name, value: id })))
);
console.log(options);

If you know for certain that there can only be one user object within each object's users array with a given id, then you can make your code more efficient by using .find() so that it returns as soon as the object user with the id is found:

const arr = [{ users: [{ id: 1, login: "alex", roles: [{ id: 0, name: "admin" }, { id: 1, name: "moderator" }] }, { id: 2, login: "bob", roles: [{ id: 0, name: "viewer" }] }] }];

const options = arr.flatMap(({users}) => users
  .find(({ id }) => id === 1)
  ?.roles.map(({ id, name }) => ({ label: name, value: id })) ?? []
);

console.log(options);

The above uses optional chaining (?.) to check that an user with the id can be found, and the nullish coalescing operator (??) to return an empty array if the id coudln't be found.

You needed to use map instead of filter on the outside array arr

flat then flattens the remaining objects

  const arr = [
    {
      users: [
        {
          id: 1,
          login: "alex",
          roles: [
            { id: 0, name: "admin" },
            { id: 1, name: "moderator" }
          ]
        },
        {
          id: 2,
          login: "bob",
          roles: [{ id: 0, name: "viewer" }]
        }
      ]
    }
  ];

  const rolesOptions = arr.map(({ users }) =>
    users
      .filter(({ id }) => id === 1)
      .map(({ roles }) =>
        roles.map(({ id, name }) => ({ label: name, value: id }))
      )
  ).flat(2);
  
  console.log(rolesOptions)

This is what I came up with:

const arr = [
  {
    users: [
      {
        id: 1,
        login: "alex",
        roles: [
          { id: 0, name: "admin" },
          { id: 1, name: "moderator" }
        ]
      },
      {
        id: 2,
        login: "bob",
        roles: [{ id: 0, name: "viewer" }]
      }
    ]
  }
];

const users = getUsers(arr)

const rolesOptions = getRolesOptions(users)

console.log(rolesOptions)

function getUsers(arr) {
  let res = [] // The result array

  arr
    .filter(({ users }) => users) // Filters to find every instance that has a "users" JSON key
    .map(({ users }) => users) // Maps out the users into multiple arrays
    .forEach(users => { // Adds each array of users into one array
      users.forEach(user => {
        res.push(user)
      })
    })

  return res
}

function getRolesOptions(users) {
  let res = []  // The result array

  users.forEach(user => {
    user.roles.forEach(({ name, id }) => { // For every user it pushes the role in formate { name, id } to the result array
      res.push({ label: name, value: id })
    })
  })

  return res
}

There probably is a neater way. Sorry if it is not what you asked for