When a Check for Updates is triggered, it connects with the Malwarebytes servers to check for the latest protection updates and product version. If you are not running the latest Malwarebytes product version, an alert displays informing you an upgrade is available. You may receive an Upgrade Available alert for both Malwarebytes Premium and Free version on Mac device.
Malwarebytes for Mac Upgrade Available alerts
Displayed in Malwarebytes for Mac.
Displayed in the macOS Notification Center