Hello!
I found out about the FTD2XX.DLL library via the list which supports the VEE program, which is now supported by Keysight. And that user was able to access the features of the library to fully inform VEE of it, and do other things. However... In my case I sometimes see error messages that a particular method isn't available, yet that's what was selected.
Supposedly the library is supposed to be registered with the Dot-Net collector of such libraries inside Windows, but I've not found a clew as to how that should be done. I did note that the C# examples shown describe how to build from the source code, and that includes making the library available at build time, and including the XML file for interpretation by Visual Studio. I've also come across on the site a Labview example series. Well okay but I use VEE for my work.