Catalina Contacts app completely blank
After a very frustrating, fruitless journey through all the online suggested fixes I could find, I eventually figured out the problem, somewhat by accident. Apparently, my system had two versions of the Contacts app installed, one that worked and one that didn't. I'm not sure how this happened but I have an idea.
I keep my frequently used apps, including Contacts, in categorized folders within the Programs system folder. I drag these folders to my dock and open everything from there. The nonfunctional version of Contacts was in the dock folder. The functional version was in its default place in the Programs folder. Maybe the docked version became 'disconnected' from the contacts system database when I upgraded to Catalina and a new version of Contacts was installed in Programs?
To fix the problem, all I had to do was delete the nonfunctional version of Contacts and move the functional one to the dock where the old one used to be. Everything works as normal now.