If you are using theme_get_settings, such as: $value = trim(theme_get_setting('my_setting')); Then in your code editor you will also be seeing undefined  function 'theme_get_setting'.  This function has been deprecated for some time.   Instead, you need to use Passing the theme.manager and theme.initialization services to theme_handler constructor as optional parameters is deprecated. These parameters are also mandatory. $theme_handler = \Drupal::service('theme_handler');Get...

Common commands Themes and plugins have similar command lines.  So rather than note them individually and miss clarity, the reference {type} can be replaced with the term plugin or theme.   install php artisan {type}:install AuthorName.PluginName  list php artisan {type}:list   refresh plugins php artisan plugin:refresh AuthorName.PluginName  Utility references   Clear cache php artisan cache:clear  Clear config php artisan config:clear  Restart...