Troubleshooting & messages · Undo, move back and Recycle Vault
Why does it warn that this is the last copy and nothing is left to restore from?
Short answer: You're removing the last remaining copy, so it's permanent — not sent to the Trash and nothing to restore from. Restore or copy it first if you might need it.
Usually removals in Storage Studio are recoverable — they go to the Recycle Vault or the Trash. This item is the last copy (for example, you're deleting it from the Recycle Vault itself), so removing it is permanent: it isn't sent to the Trash and there's nothing left to restore from.
If you might need it, restore it first or copy it somewhere safe.