How to make node URL alias mandatory in Drupal 8 and Drupal 9

You can use the following code snippet to change the required attribute of the path field in the node form alter in this way:

/**
 * Implements hook_form_FORMID_alter().
 */
function example_module_form_node_form_alter(&$form, &$form_state) {
  $form['path']['widget'][0]['#open'] = TRUE;
  $form['path']['widget'][0]['alias']['#required'] = TRUE;

}

This will keep the path tab open by default and mark the alias field as required.