On previous OS versions, the FTDI serial USB bridge VCP driver support came from FTDI via FTDIUSBSerialDriver.kext. This was then replaced by inbox Apple driver AppleUSBFTDI.kext.
In both of those cases, custom USB device IDs (VID/PID) could be supported by creating a wrapper kext that declared the custom IDs and referenced the actual underlying driver package/binaries.
In Catalina, AppleUSBFTDK.kext is gone, and native FTDI device IDs are now supported by DriverKit.AppleUSBFTDI.dext. The FTDI driver and/or custom ID wrapper KEXTs can be manually loaded using kextutil, but they do not automatically load when the device is plugged in. It seems that DriverKit.AppleUSBFTDI.dext is servicing all such serial USB devices now? But the Info.plist for that .dext only lists the native FTDI device IDs.
Is there any guidance on how to support custom IDs for the FTDI devices in Catalina? Creating a dext wrapper does not seem to be the right idea, as I am seeing lots of info stating that .dexts must be part of an application now, that there is no such thing as a standalone dext.