Your site is down. First check the database details in wp-config.php and check...

https://smoothdecorator.com/how-to-test-database-credentials-without-wordpress-loading/

Your site is down. First check the database details in wp-config.php and check for a hosting outage. If those are right, repair the database and review server logs. Contact hosting support if the database service is unavailable or you cannot access it.