There are two different main approaches, with and without access to the Internet. These notes are for using reposync to create an “offline” installation from RPMs with dependencies.
sudo subscription-manager repos --enable rhel-9-for-aarch64-baseos-rpms --enable rhel-9-for-aarch64-appstream-rpms
sudo dnf install yum-utils
sudo reposync -m --download-metadata --gpgcheck -p /path/to/download
Note that reposync requires a huge amount of bandwidth and preferrably speed. Not something to try with less than 100mbps connection.
Related: