Your ESET product notifies you with an icon and displays the notification "Operating system is not up to date"
Disable macOS update notifications
ESET products are designed to notify you of important updates to your operating system that might contain important patches or bugfixes. These notifications can be disabled in your ESET product, however doing so will not disable the macOS update process or notifications originating from the macOS itself.
Windows users: click here
Open ESET Cyber Security or ESET Cyber Security Pro. How do I open my ESET product?
Click Setup → Enter application preferences.
Click Alerts and Notifications.
Click Setup next to Advanced Options.
Deselect the check box next to Operating system updates and click OK.