Great! Thanks for your advice. For now, I'll just rely on iOS preventing multiple instances natively, and LSMultipleInstancesProhibited on macOS (even if it's not 100% reliable).

My apologies for the 3 duplicate messages!! When I pressed comment it said something about "unable to save"

If a user signs out of iCloud to hand over their device to someone else, they’d have to go through each app and check if the last export date is after their last change. If it wasn’t, they’d have to wait an arbitrary amount of time before NSPersistentCloudKitContainer decides to sync — sometimes hours. This design seems cumbersome at best and dangerous overall.

If a user signs out of iCloud to hand over their device to someone else, they’d have to go through each app and check if the last export date is after their last change. If it wasn’t, they’d have to wait an arbitrary amount of time before NSPersistentCloudKitContainer decides to sync — sometimes hours. This design seems cumbersome at best -- and could easily cause data loss.

If the user was signing out of their account to give to someone else, then they'd have to ensure for all their apps that changes have been synced. As a developer, we could add an indicator stating the last export date. The user would have to go through each app and check that the last export date was after their last change, and if it wasn't, they'd have to wait an arbitrary amount of time before NSPersistentCloudKitContainer syncs (sometimes hours). This seems cumbersome at best for users.