Advanced users can fetch the full installer using the command:
The quickest way to check for supplemental updates or security patches for 10.15.7 is through your system settings:
A: Network instability or Apple’s server throttling. Try a wired Ethernet connection, or use the combo updater instead of the full installer.
While the App Store often provides a small "stub" installer, you can force the download of the complete 8GB+ file using Terminal on a Mac already running Mojave or newer.
Below it, a small terminal prompt blinked:
