I am having the exact same issue except my new windows are white boxes. It happens with anything Core Shell generates - even if I try to open "About Core Shell". Doing a Command-N for new window just makes more empty white boxes. This may have something to do with the Core Shell helper app which had to be upgraded after the upgrade to Core Shell 2.2. This issue started immediately after the helper update. Could this be Gatekeeper interfering?
My system is a 5K Late 2015 iMac running Catalina 10.15.5.