Shadow and highlight clipping not working

Lightroom CC version 5.0

MacOS 12.0.1

I select a raw file, originated on a Sony A7riii.

I turn on the shaddow and highling clipping in the histogram. On ajusting the whites/blacks sliders no clipping colours are showing. This was working in the previous version of lightroom.

If I hold down the option key and move the sliders the screen image goes all black if I move the whites slider, and white if I move the blacks slider.