The php_mysql module is deprecated for oooold time, now for php 5 and 7 require php_mysqlnd and MySQLi.General Error
SQL ERROR [ mysql4 ]
mysql_connect function does not exist, is mysql extension installed? 
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From https://php.net/en/mysql_connect :
When phpbb3 support the non deprecated functionality for connect to database without manualy modifications?This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information