Healing Brush Tool

LrC 13.3.1

macOS Sonoma 14.5

Problem: Develop Module - Healing Brush Tool (Q):

The Visualize Spots checkbox in the Toolbar below the photo that I'm editing has disappeared!
Of course, pressing the A key allows me to Visualize Spots BUT the Slider that reveals more dust spots (when moving Slider to the right) or less dust spots when moving Slider to the left is NO LONGER THERE! The only Sliders visible in the Toolbar below the photo are Zoom and Show Grid.
I have checked this on both my Macs, both are on latest LrC version and the same issue is on both machines.