Settings::getExtConf() 

\nn\t3::Settings()->getExtConf($extName = ''); 

Get extension configuration. come from the LocalConfiguration.php, are defined via the extension settings defined in the backend or ext_conf_template.txt

Earlier: $GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['your_extension_key']

\nn\t3::Settings()->getExtConf( 'extname' );

| @return mixed

public function getExtConf( $extName = '' )
{
	return GeneralUtility::makeInstance(ExtensionConfiguration::class)->get($extName) ?: [];
}