Warning "PHP extension mysqli not loaded" when using PostgreSQL
If you use TYPO3 on a server with PostgreSQL which does not have the mysql php extensions installed the Install Tool complains about
PHP extension mysqli not loaded TYPO3 CMS uses PHP extension mysqli but it is not loaded in your environment. Change your environment to provide this extension.
When using a PostgreSQL that extension is not necessary. The warning should only be displayed if a MySQL Connection is configured.