Unset email address requirement on User Form not taking
The email field is one of the entity fields added by User::baseFieldDefinitions(), which sets it with a constraint.
$fields['mail'] = BaseFieldDefinition::create('email')
  -&gt;setLabel(t('Email'))
  -&gt;setDescription(t('The email of this user.'))
  -&gt;setDefaultValue('')
  -&gt;addConstraint('UserMailUnique')
  -&gt;addConstraint('UserMailRequired')
  -&gt;addConstraint('ProtectedUserField');

The UserMailRequired constraint does what its name suggest: It checks if the user's email address is provided if required. It isn't required if the account originally had no mail set and the user editing the account has the administer users permission.
That constraint needs to be removed from the entity field, to allow the email field to be empty. (It still necessary to mark the email form field as not required, though.)
use \Drupal\Core\Entity\EntityTypeInterface;

function mymodule_entity_base_field_info_alter(&amp;$fields, EntityTypeInterface $entity_type) {
  if ($entity_type-&gt;id() == 'user' &amp;&amp; !empty($fields['mail'])) {
    $constraints = $fields['mail']-&gt;getConstraints();
    unset($constraints['UserMailRequired']);
    $fields['mail']-&gt;setConstraints($constraints);
  }
}