[Bug]: 'enforce_theme' => 'highcontrast', and also any other setting does not work

I use the setting described here:
https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/config_sample_php_parameters.html

  1. put ‘enforce_theme’ => ‘highcontrast’, inside nextclouds config.php
  2. restart the nextcloud server
  3. I cannot change the theme anymore, BUT I still have the theme from before, not the configured theme