David MoonI updated iMac to Catalina and then wanted to retrieve a year old file via Time Machine only to find Time Machine only went back to the start of Catalina. Looking online it appears that Catalina changes the Time Machine file to .backupbundle in place of the previous .sparsebundle. When I restarted Mac on Mojave clone it could not find time Machine. It's not the end of the World in my case but a nasty surprise. Here is a link on the subject.