When Time Machine made its backups to an HFS+ volume, there was a great deal you could do with those backups and their storage, including making a complete copy of them, and deleting large items from inside a backup. This is because those backups were basically just a structured set of files, folders and hard links.
Now that Time Machine is making its backups to an APFS volume in Big Sur and later, those backups have changed, becoming synthetic snapshots, which aren’t amenable to the manipulation you could perform on an HFS+ volume. This has left many users puzzled as to why these new backups don’t work ‘properly’. This article explains what they can do, and what they can’t, things that Apple doesn’t tell us, and even Apple Support seems worryingly vague about.
Read more at eclecticlight.co