I'm still trying to untangle my Aperture photos and export them to Adobe Lightroom before upgrading my OS from Mojave to Catalina. (Side note: Boo to Apple for dropping Aperture! I obviously had trouble managing my files, but I far prefer the interface to Adobe.)
I don't know how the update was downloaded, but now it is prompting me to restart and install. Can I remove the download, or somehow postpone the update? I'm worried that it will automatically install the next time the computer reboots. I'll try to avoid this, but know it sometimes happens inadvertently.
I have an early 2013 MacBook Pro (15" Retina) running Mojave 10.14.6.