Hey, check this out. Apparently, there is a mechanism in MacOS Catalina that allows you to revert the Catalina install to your previous OS. Catalina uses the APFS snapshot feature to take a snapshot of your Mac when it is upgrading it. If you encounter problems with Catalina, you can use that snapshot to revert to your old system if you do it within 24 hours. Check out the second section in this article for more information. I had no idea you could do this. It makes updating to Catalina a little less risky.