In macOS Catalina 10.15.4 and later, Apple displays the notification below when McAfee applications load system extensions on the macOS system. In 2019, Apple informed developers that macOS Catalina is the last macOS that fully supports legacy system extensions. McAfee is working on this transition in our applications.

The macOS systems display the following message until the transition is completed:

Legacy System Extension
Existing software on your system loaded a system extension signed by "McAfee, Inc." which will be incompatible with a future version of macOS. Contact the developer for support.

This message displays when a legacy system extension is loaded for the first time. It also displays periodically while the extension remains in use.

For more information about this notification, see the following Apple Knowledge Base article: https://support.apple.com/en-hk/HT210999.