I have just downloaded Elements 2021. I have my photos arranged in 3 catalogs but Elements has only recognised and imported one of them. How do I find the others to import them? I am running the program on a Mac using osCatalina.
When you click on the 'convert' button, the organizer searches for other catalogs in the default location and shows the full list of those catalogs. You may have to tick the option to also show already converted catalogs. If you don't find a catalog (for instance it's in a custom location on another drive) you have to navigate to the real location of that catalog (button to show more).
You can do a search in the finder for files named 'catalog.pseXXdb', XX being the version number of the catalog, ie catalog.pse18db for PSE 2020. The catalog folder includes this database file.
I am a Windows user, I don't know if there is something specific to Macs or Catalina.