New Cintiq 16 shows cursor but otherwise just a black screen (Ubuntu 20.04)

I have a new Cintiq 16 and it powers on just fine. I can see the device under Displays settings and it is recognized. I've arranged it as my 3rd monitor and both the number 3 shows up on the tablet and the cursor is visible when I move the pen around. OTher than these, it's just a black screen. How do I configure it to mirror one of my other monitors?