security update for iMac

Go to System Preferences > Software Updates. If you are prompted to Upgrade to Catalina or Big Sur and wish to stay on Mojave, look right below the prompted Upgrade box for More Updates in blue.

You can also find the latest stand-alone Mojave security update at > https://support.apple.com/downloads

Hi ronrbev,

Unless there is an update in System Preferences > Software Update, there are none.

You should also really consider upgrading. Upgrade to macOS Catalina, How to get old versions of macOS - Apple Support, or if you have a 2014 or newer iMac, upgrade to macOS Big Sur: How to upgrade to macOS Big Sur - Apple Support.

Cheers,

Jack