If you have a device running Windows 10 version 2004 with a built-in screen (such as a laptop or tablet) and a connected external display set to Duplicate your primary screen, you might see both monitors flicker and the external monitor go black if you try to draw using an Office app (such as Word). This can also happen with some other apps capable of drawing, such as Whiteboard. If you check in Device Manager, your graphics controller will have a warning icon next to it (a yellow triangle with an exclamation mark in it).
The external monitor should recover if you restart your device.
Microsoft has confirmed that this is a problem in Windows 10 version 2004. We are working to fix the issue in a future version of the operating system.