dbconnect.php have been removed in WHMCS 6.0

As of 6.0 however, any scripts which still rely on including the dbconnect.php file to function will need to be updated to instead include the init.php file. When including the init.php file, it is not necessary to include any other WHMCS files.

so if you have any module that contains dbconnect.php you can change it to init.php