To be exact, Composer allows you to install packages which don't have a license, but you cannot publish a package on Packagist anymore if it does not have a lic

To be exact, Composer allows you to install packages which don't have a license, but you cannot publish a package on Packagist anymore if it does not have a license (and packages which were submitted before the license became required are not updated anymore in the registry until they specify the license)