When you are sure that all 'Cloud' photos have downloaded into the Lightroom-Classic catalog (and a local hard-drive as set in Preferences)- SYNC SETUP IN CLASSIC
It requires removing the original from the cloud, and then syncing the same image again from Lightroom Classic so it becomes a smart preview in the cloud by this method-
1: Remove the image(s) from the "All Synced Photographs" collection in Lightroom-Classic.
2: Wait till they have disappeared from the cloud. *
3: Add them again to the "All Synced Photographs" collection in Lightroom-Classic, or to a synced collection (if you want them in a particular album on your iPad).
4: The image(s) will now sync to the cloud again, but this time as smart previews.
* If you go to https://lightroom.adobe.com you can view "Deleted" files that remain in the Cloud for 60days.
Or to force an immediate Delete- Select the files shown in "Deleted" list and Bin them.
Regards. My System: Lr-Classic 12.3 Photoshop 24.5, ACR 15.3.1, Lightroom 6.3.1, Lr-iOS 8.0.8, Bridge 13.0.3, Windows-11.