
The data migrated successfully for the most part (except my Contacts which is a whole other story).

sparsebundle, erased the SSD again, installed Mojave and presto, the previous Mojave backup was visble again. So, erased again, installed Catalina, and after browsing the Time Machine backup in Finder, I could see the old backup there, changed the file extension from. This stopped Time Machine on Mojave from being able to show me the backup to select (imagine my heart rate). When I chose to erase the SSD, and install Mojave again, Catalina appeared to have changed the file extension of the backup from. In the brief period of time I had Catalina it made maybe 1 or 2 Time Machine backups. Select that (in my example 'Time Machine Backups') and click Continue. After a search it should show you the Time Machine Backups directory as a volume that contains your backup. When I installed Catalina I chose to migrate data from the Time Machine backup of Mojave which was successful. How To Restore Os X From Time Machine Backup Mac How To Restore Os X From Time Machine Backup Software Select Restore From Time Machine Backup and click Continue. In my experience the data (minus the OS) should come back to Mojave but it may not be visible in the list of backups to choose from when choosing a backup source during the install.

I did the same thing by using a USB installer and migrated data from the Time Machine backup during the install (it's one of the choices during the install).
