Is it still not possible to choose a minor (e.g., 12.0.7) over a major (e.g., 13.0.2) upgrade? My 12.0.6 installation only offers 13.0.2.
The priority is defined by the release channel you have chosen (https://nextcloud.com/release-channels/). By default it is stable and they probably switched to NC13 already. I don’t know the exact policy when this switch is made, you can try to change to the production channel on your admin page.