Folders lost after upgrade from Lightroom to Lightroom

Important to realize that Lightroom CC contrary to Lightroom Classic (i.e. what you were used to) does NOT use a folder structure. All files are stored in the cloud and not in a folder structure. The trick described above creates a album structure that mimics the old folder structure. It does not get you an actual folder structure. If you want a folder structure on your local hard disk, you should not use Lightroom CC but use Lightroom Classic.

As indicated in the link on that Jon posted, to retain the folder structure, you need to create Collections from them (either drag them into Collections or Right-click (Windows) or Control-click (macOS) and choose Create Collections From Selected Folders)

I think your only option is to clear the migrated photos from the Cloud and re-migrate, but I think you would have to rename the migrated Catalog (as a Catalog can only be migrated once**)

**unless you either delete, move or rename (just as a backup) Lightroom Library.lrlibrary in Pictures folder on Mac and in Username\AppData\Local\Adobe\Lightroom CC on Windows. Although check that any other photos, for instance Mobile Uploads are backed up.

Refer to the FAQ and preparations for migration:

Migrate photos and videos from Lightroom Classic CC to Lightroom CC