anytime i try and mask with the brush tool my mac freezes and the rainbow icon appears it happens after every couple strokes, making masking almost completley impossible. i thought it was my memory so i upgraded to 16GB of memory on my imac, howver that did not fix anything.
Sorry that Lightroom Brushes keep freezing the app. Which version of Lightroom are you using? Does the app freezes while using Adjustment brush on all the images? Also, are you running the Mac OS Catalina on your iMac?