A computer feature or peripheral that has completely stopped should be separated into driver, permission and physical-connection layers before assuming component failure. For Mac iCloud Drive sync, first check sync status and verify a file on iCloud.com before moving or deleting it.
What this covers
- Mac iCloud Drive sync with this exact failure state
- Diagnosis across cloud capacity/account versus local storage, network and optimization state
What it does not cover
Try in this order
0 of 4 completedCapture the exact failure state
ReversibleCheck Device Manager or System Information for whether the hardware is even detected, and whether an error code is shown. Expected behavior: reconcile Desktop, Documents and app files with the intended Apple Account.
Isolate the component boundary
ReversibleCheck sync status and verify a file on iCloud.com before moving or deleting it. Test the peripheral on a different port or user account, and test a different peripheral on the same port. Boundary to separate: cloud capacity/account versus local storage, network and optimization state.
Correct only the proven cause
ReversibleCorrect quota/network or let sync finish on power; preserve local copies first. Reinstall or roll back the driver, or grant the missing app permission.
Verify and stop safely
ReversibleConfirm the feature works after a full restart in at least two different applications. Never disable Desktop/Documents sync or delete files until another copy is verified.
Evidence ledger
Sources behind this answer
Exact questions