I have done this with an artist drawing on an iPad Pro with apple pencil with a drawing app called Procreate.
The iPad is connected to the mac with AirServer (making the mac an AirPlay receiver) and then from AirServer to VDMX with syphon.
Procreate has a mode which allows you to have second screen sent out via AirPlay without any gui from the app.
I have also done this with photoshop and captured the window and sent it to VDMX