backing up iPhone gets spinning arrows

I'm trying to back up my iPhone 6s to my Mac. I've just installed Catalina, so I'm backing up through Finder. The process seems to have stalled, because I am getting endless spinning arrows (not the wheel) instead of a progress bar or progress circle. Any ideas on what is going wrong here? I did successfully download some images to Photo, but nothing else seems to be working properly. I should add that the Sync button and back up button are grayed out, and that I appear to limited ability to interact with the iPhone at all while open in the Finder. I can check for updates, and click some buttons, but can't apply any changes.