There are several ways.
One way is to use TeamViewer for connecting your iPad (whatever the model you have) to your computer (whatever the os you have) and share the window as you usually share a window.
If you have a MacBook or an iMac or a Mac mini, just connect your iPad with a cable and launch sidecar :then if you drag your BBB window on the iPad screen, you will then be able to use the stylus in the BBB window and, in particular , with the whiteboard or share any windows that will be on your IPAD's screen (the stylus interacts with this screen).