Ok, I think I have this nailed down.
On my one system I was able to very easily switch to the WinUSB driver using ZADIG but on my other two system I completely failed. ABCD567’s post reminded me that these RTL devices should be treated as a composite devices and the ZADIG needs to replace the driver for the composite, not the two individual devices.
Normally, the FlightStick will show as two devices in Device Manager. If the automatically downloaded drivers from Microsoft are used the Flightstick will be seen as a HID Infrared Remote Receiver under Human Interface Devices and as a Realtek 2832U device under Sound, video and game controllers.
The trick to getting this to work is of course ZADIG.
1. Download Zadig.
https://zadig.akeo.ie/2. Run ZADIG as Administrator
3. IN Options -- Check "List all Devices" , UNCHECK "Hide Hubs or Composite Devices"
4. From the drop down, look for the composite device RTL2838UHIDIR (Composite Parent)
5. Change the Driver of the COMPOSITE Driver to WINUSB, press the “Replace Driver” button
6. The 2 previously mentioned devices will disappear from Device manager and the new RTL2838UHIDIR device will appear under Universal Serial Bus Devices
7. Reboot.
8. Start RadarBox and your FlightStick should be discovered.