Premiere Pro Beta Object Mask Not Finding Anything to Mask



Windows 11 Home
Version 10.0.26100 Build 100
I believe I've followed all the correct instructions for this version here: https://helpx.adobe.com/premiere-pro/using/object-masking.html
The problem: When I select any of the masking tools from the Object Mask on the toolbar, the results are the similar. When I use the Object Mask, I hover over the clip in the display window, and... it finds nothing. When I use the rectangle or ellipse tool, nothing happens when I go over the display.
Is there a step I've left out?
This could be a very useful feature for me since the studio where I record my video performances is so tight that it is impossible to get a shot of me playing my grand piano without the keyboard of my upright showing in the lower left corner...