This program will create a executable which can launch MS Whiteboard. Then you can map this executable to any 3rd party legacy application to launch the same.

MicrosoftWhiteboardLauncher.cpp

// This program will create a executable which can launch MS Whiteboard.
// As the Whiteboard is now a Windows Store App it's hard to map it to a 3rd part software like Huion tablet interface, so you can compile and map this binary instead to the 3rd party client, which in turn will launch whiteboard for you.
// This code is not that big of a deal, hence there is no need for any License. Use it as you wish. 

#include <iostream>
#include <stdlib.h>
int main() {
    std::system("start shell:appsfolder\\Microsoft.Whiteboard_8wekyb3d8bbwe!Whiteboard");
    return 0;
}