I know Catalina support is just being really focused on now, but FWIW starting with b7 on Catalina 19A546d (beta 7), no databases will sync from iCloud. DT3 doesn’t even see the databases in the iCloud sync store.
DT3b7 on a 10.14 machine sees them fine. DT3b6 on Catalina B7 also saw them fine.
I did download the new version that was mentioned in the thread about not being able to create new databases, but that did not fix this problem.
Figured someone should know, unless its peculiar to me!
I’m fairly confident I rebooted as a diagnostic measure, but possibly not after installing the corrected version of B7. Unfortunately I left my dev machine at home today, but I’ll check it tonight for sure.