Rich Trouton:

As part of macOS Catalina 10.15.4, Apple has begun displaying a new dialog window message concerning third-party kernel extensions. macOS Catalina is the last macOS to fully support the use of kernel extensions and these messages are meant to notify users of the following:

• macOS had detected that a third-party kernel extension had been loaded.
• The loaded kernel extension would be incompatible with an unspecified future version of macOS

There are some additional details on Apple’s site:

In 2019, Apple informed developers that macOS Catalina will be the last macOS to fully support legacy system extensions, and we’ve been working with developers to transition their software. By moving beyond these extensions, developers are helping to further modernize the Mac, improve its security and reliability, and enable more user-friendly software distribution methods. A final transition date has not yet been set.

Until the transition is complete, your Mac displays a message when a legacy system extension first loads, and again periodically while the extension remains in use. This gives you advance notice that existing software on your system loaded a system extension that will be incompatible with a future version of macOS:

…and on Apple’s developer site:

System extensions on macOS Catalina (10.15) allow software like network extensions and endpoint security solutions to extend the functionality of macOS without requiring kernel-level access. At WWDC19, we announced the deprecation of kernel extensions as part of our ongoing effort to modernize the platform, improve security and reliability, and enable more user-friendly distribution methods. Kernel programming interfaces (KPIs) will be deprecated as alternatives become available, and future OS releases will no longer load kernel extensions that use deprecated KPIs by default.

This will be a rocky transition for a bunch of users, especially in the enterprise.