I was not aware of the Catalog backup procedure before I reformatted my Mac hard drive while installing Catalina. I backed up the disk with Carbon Copy Cloner as a non-bootable clone. How can I locate the Adobe Photoshop Elements 2016 catalog file? It's not in the default location: /Users/[Your User Name]/Library/Application Support/Adobe/Elements Organizer/Catalogs. What is the file type? Thanks.
The catalog is a folder named with the name of the catalog as shown in the organizer; it's not a single file.
I don't think it can be elsewhere than the default location, otherwise you would have located it elsewhere purposely. The catalog folder may be elsewhere if you have backed up and restored your catalog and library, but since you did not know the procedure, that is unlikely.
The key test to find the catalog is to do a search for the main database in the catalog folder. It's called catalog.pse15db for PSE15, catalog.pse16db for PSE2018 (there is no PSE2016 version).
If you find it, you can convert it in PSE2020 from the catalog manager in the organizer.
The problem will be that the organizer will not see the links to the media files restored from Carbon Copy as the original locations. I believe all files will be shown as 'missing' or 'disconnected'.
Note that I don't know anything about Macs or Carbon Copy.