Steps for Enabling or disabling maintenance mode using Drush
1. Run the following Drush commands to enable maintenance mode and clear
drush state:set system.maintenance_mode 1 drush cr
2.Run the following Drush commands to disable maintenance mode and clear the cache:
drush state:set system.maintenance_mode 0 drush cache:rebuild
After running either set of commands, verify that your site is either in or out of maintenance mode by visiting the site in a browser where you are not logged in.