Last update February 02, 2023
You cannot use directly Midi Learn option in D16 plug-ins with FlStudio, because this host application filters Midi CC messages comming from midi controller. You need to use Midi out track in FLStudio and connect it with a plug-in and hardware controller, to build way around. This way of using MidiCC in FLStudio concerns not only D16 plug-ins, but all VSTs responding for MidiCC messages.
Add a Midi out track in FLStudio
Set the same Midi port number in Midi out track's properties and plug-in's window
Click the mouse right button on a first controller of Midi out track, choose Configure item.
Set a MidiCC number the Midi out track will be sending to plug-in and click Accept
Now You need to connect first controller of the Midi out track with a hardware controller. Click the mouse right button on a first controller of the Midi out track and choose Link to controller item
Then tweak any knob of Your hardware controller. Now You're ready to assign this controller using Midi Learn mode in plug-in