Shape tool in Layer Mask

I've just upgraded to Elements 2020, and I'm trying to do what I feel like I've always done (occasional, not pro, photo editing). I've created a Layer Mask and Inverted the mask, then I usually will grab the Shape tool and draw a white Rectangle or Ellipse. However, this time, the shape doesn't get applied to the Mask, instead, it auto-creates a new layer. 

My paintbrush will effect the mask, but not the shape tool. I've also been able to use the Marquee tool to draw the shape I'd like, and then fill with the paint bucket, but this is not ideal. 

Anyone know why the Shape tool won't draw onto the Layer Mask.