Apple is phasing out iCloud Documents and Data.
Apple will completely replace the service with iCloud Drive in May 2022.
Users will need to enable iCloud Drive to view files in iCloud Documents and Data.
Apple has confirmed that it will phase out iCloud Documents and Data, replacing it completely with iCloud Drive in May 2022.
In a support document spotted by MacGeneration Apple states:
In May 2022, iCloud Documents and Data, our old document syncing service, will be discontinued and completely replaced by iCloud Drive. If you use iCloud Documents and Data, your account will be migrated to iCloud Drive after that date.