I've already tried several tutorials, but I still couldn't create a user with a name to, for example, send the email in the tag %DISPLAY_NAME%

Here is the code I use to register users if it helps to solve the problem, if you have more doubts please send them in the comments

function register () {
  // Get all our input fields
  email = document.getElementById('email').value
  password = document.getElementById('password').value
  auth = document.getElementById('auth').value
  favourite_song = document.getElementById('favourite_song').value
  milk_before_cereal = document.getElementById('milk_before_cereal').value

  // Validate input fields
  if (validate_email(email) == false || validate_password(password) == false) {
    alert('Email or Password is Outta Line!!')
    return
    // Don't continue running the code
  }
  if (validate_field(auth) == false || validate_field(favourite_song) == false || validate_field(milk_before_cereal) == false) {
    alert('One or More Extra Fields is Outta Line!!')
    return
  }
 
  // Move on with Auth
  auth.createUserWithEmailAndPassword(email,auth, password)
  .then(function() {
    // Declare user variable
    var user = auth.currentUser

    // Add this user to Firebase Database
    var database_ref = database.ref()

    // Create User data
    var user_data = {
      email : email,
      full_name : full_name,
      favourite_song : favourite_song,
      milk_before_cereal : milk_before_cereal,
      last_login : Date.now()
    }

    // Push to Firebase Database
    database_ref.child('users/' + user.uid).set(user_data)

    // DOne
    alert('User Created!!')
  })
  .catch(function(error) {
    // Firebase will use this to alert of its errors
    var error_code = error.code
    var error_message = error.message

    alert(error_message)
  })
}