Not usable with typo3/cms-composer-installers v4
In an installation which uses typo3/cms-composer-installers v4 already, the following error is displayed:
Error! (cant open "/var/www/html/public/typo3conf/ext/")
The path "typo3conf/ext" does not exist anymore when using typo3/cms-composer-installers v4, every extension is stored now in the "vendor" folder outside the public folder.
More information: