Converting from LR to LR Classic

You can't "convert" the LR catalog in order to get it into LrClassic. What you can do is turn on syncing in the LrClassic catalog, and a copy of ALL images that have been stored in the cloud will be downloaded into that Classic catalog (which include all the edits apart from keywords and location data). Before doing that, however, visit the LrClassic Preferences>Lightroom Sync tab where you can specify the location for those downloaded images (and you can even select one of the date-based folder structures). If you elect not to change the location, the default will be an obscure location in the Pictures folder on your system drive.