Select and Mask in Photoshop CC not working on Mac OS Big Sur 11.5.2

Im using Lightroom v4.4 and Photoshop v22.5.1 and Select and Mask function is not working as it used to.

I copy my Background layer.

On the copy of the Background Layer I choose " Select and Mask"

I then choose " Select Subject"

The shape I want to cut out is highlighted

I then select ok

The result is that I am presented with the layer with the subject highlighted but the layer does not include the mask. See screen capture.

I can copy the subject and paste it on to a new layer but am unable to refine the mask.

Any ideas please - am I doing something wrong or is this a known issue?

Thanks