Indesign cannot handle the request because a modal dialog or alert is active

I have the latest InDesign 2020 running on a Mac. I can open documents okay, but every time I open the colour picker and try to use the eye dropper, InDesign freezes and I get the message 'Indesign cannot handle the request because a modal dialog or alert is active'. I then have to quit InDesign and reopen to carry on working. It's doing it with every document. I've tried force quit, restarting my computer, and even uninstalling InDesign and reinstalling it, but it's still happening. Any way to fix this irritating problem? Thanks.