material_base-8.x-2.x-dev/material_base.post_update.php

<?php

/**
 * @file
 * Update functions for the material_base theme.
 */

/**
 * Install stable9 and uninstall material_stable9 themes.
 */
function material_base_post_update_9301(): void {
  $theme_installer = \Drupal::service('theme_installer');
  $theme_installer->install(['stable9']);
  if (\Drupal::service('theme_handler')->themeExists('material_stable9')) {
    $theme_installer->uninstall(['material_stable9']);
  }
}