I backed up all the catalogs from my old computer with PE18. All restored and converted successfully on the new computer with PE19.
However, I cannot see any of the catalogs when I open the Manage Catalogs dialog. I can browse my way to the directory on the external hard drive, select a catalog and manually open it in Organizer. Why can't I see the list of catalogs as I have in all previous releases of PE?
When you restore a backup on another computer (in 'custom' location), the catalog folder is restored just under the master folder you have chosen. It is 'converted' after all media files have been restored. The old converted catalog folder keeps the same name as the newly create one, with a '-1' suffix.
The database file in the catalog folders of PSE2018 are called 'catalog.pse16db' and for PSE2019, they are called 'catalog.pse17db'. You can do an explorer search to find all the databases and the catalogs they are in.
The catalog manager has the option to move the catalog folders back to the default (hidden) location on the system drive. Or you can move them back manually from the explorer.
The location of an open catalog is given in the menu Help >>System information.