From Adobe:
Issues fixed in Lightroom Classic CC 7.3.1 (April 2018 release)
Known issue
(Only on macOS) When backing up your catalogs on macOS, Lightroom Classic doesn't compress (zip) catalogs that have a file size less than 4 GB. As a workaround to this issue, manually compress the backed up catalog files. Compressed files take up less hard disk space. By default, Lightroom Classic saves backed up catalogs to the following location on macOS:
/Users/[user name]/Pictures/Lightroom/[catalog name]/Backups
B&H carries Adobe Photography Plan subscriptions.
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