In the ACR color range mask, I can't expand the range by using Shift + click to add samples as suggested in the text under the Refine slider. Likewise, once the color range is selected, I can't click in a different spot to cancel the original selection and make a different selection. The cursor changes from an eyedropper to an arrow once the original selection is made.
I've tested this using ACR 14.0. I've tested this on a 2020 Mac Mini M1 Running the lastest MacOS and on an iMac 2012 running Catalina 10.15.7.