Di nuovo, sì, hai cancellato tutte le istantanee locali. Ma hai chiaramente un'unità esterna Time Machine. E le istantanee di Time Machine (locali o remote) pongono determinati requisiti sull'unità di origine. Da man tmutil :

BACKUP STRUCTURE
     Throughout this manual, specific language is used to describe particular
     "realms" associated with Time Machine backups. It is important to under-
     stand this terminology to make effective use of tmutil and its manual.

     backup source
             A volume currently being backed up by Time Machine.

     backup disk
             The HFS+ volume that contains Time Machine backups.

     backup destination
             In the case of a local destination, a synonym for backup disk.
             For network destinations, this is the AFP or SMB share on which
             the backup disk image resides.

     backup disk image (or backup image)
             A sparsebundle that, when mounted, is the backing store for a
             volume that is a backup disk.

     backup store
             The top-level "Backups.backupdb" directory at the root of a
             backup disk. E.g.,

             /Volumes/Chronoton/Backups.backupdb

     machine directory
             A directory inside a backup store that contains all the backups
             for a particular computer. For local destinations, a backup store
             can contain multiple machine directories, all for separate com-
             puters. E.g.,

             /Volumes/Chronoton/Backups.backupdb/thermopylae

-

Ricorda l'errore?

E.g., (probabilmente causato dall'utilizzo dell'istantanea APFS da Time Machine) ?

Leggi questo:

     snapshot
             A directory inside a machine directory that represents a single
             initial or incremental backup of one computer. The word "snap-
             shot", in most contexts, is a generic term and is not to be con-
             fused with a "local Time Machine snapshot", which is simply a
             snapshot stored locally on the computer. E.g.,

             /Volumes/Chronoton/Backups.backupdb/thermopylae/2011-07-03-123456

     snapshot volume
             A directory inside a snapshot that represents a single initial or
             incremental backup of one backup source. E.g.,

             /Volumes/Chronoton/Backups.backupdb/thermopy-
             lae/2011-07-03-123456/Mac HD

VERBS
     Each verb is listed with its description and individual arguments.

     destinationinfo [-X]
             Print information about destinations currently configured for use
             with Time Machine. For each backup destination, the following
             information may be displayed:

             with Time Machine. For each backup destination, the following
             information may be displayed:

                 Name          The volume label as shown in Finder.
                 Kind          Whether the destination is locally attached
                               storage or a network device.
                 URL           In the case of a network destination, the URL
                               used for Time Machine configuration.
                 Mount Point   If the volume is currently mounted, the path in
                               the file system at which it was mounted.
                 ID            The unique identifier for the destination.

             When more than one destination is configured, the most recent
             backup destination will be marked with the > indicator.

             When the -X option is provided, output will be printed in XML
             property list format.

     removedestination identifier
             Remove the destination with the specified unique identifier from
             the Time Machine configuration. Requires root privileges.

             To obtain the unique identifier for a destination, see
             destinationinfo.

A. L'errore:

Error: -69521: Your APFS Container resize request is below the APFS-system-imposed minimal container size (perhaps caused by APFS Snapshot usage by Time Machine)

B. La tua risposta:

I have removed all local time machine snapshots but I am still getting the same output.

C. La documentazione:

La parola "istantanea", nella maggior parte dei contesti, è un termine generico ed è da non confondere con uno "snapshot di Time Machine locale" .

Capisce?

Sì, hai cancellato tutte le tue istantanee locali. Ma hai anche un'altra unità di backup. Nell'esempio che hai collegato, non esisteva tale unità.

È necessario rimuovere tutti i backup di Time Machine, disabilitare tutte le destinazioni, ecc. È possibile riassociare i backup in un secondo momento. Ma seguendo questo, dovresti stare bene; Nel peggiore dei casi, decrittografa anche il tuo disco (la crittografia APFS è complicata e ha un sacco di overhead a causa del sistema key-drive / sistema user-key).