Spot removal Tool - no circle on picture

I am using Lightroom 5.7 On a Mac using macOS Catalina. I updated the Mac when it first became available.

I have used Lightroom for years. Recently I wanted to use the Spot Removal tool. Never had a problem previously.

I click on the tool the circle with arrow lights up but when I attempt to move it over a photo it disappears. It does work, but I have no idea where the circle arrow is as I cannot see it.

Please advise.

Thank you

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