An additional APFS volume can give a project its own named location without dividing a healthy container into fixed partitions. It still shares the same underlying device, so it is an organisation choice rather than a second independent backup.

This workflow is for a healthy external work drive already using APFS. Back up its existing files to another device and verify representative files before changing its layout. Do not use it as a recovery experiment on an unreadable disk or as an instruction to alter a managed backup destination.

Plan the capacity boundary

Apple explains that APFS volumes in one container share available space. A volume grows as it stores data; seeing several volume names does not mean each has the full container capacity reserved exclusively for it.

When adding a volume, Size Options can set a reserve, which guarantees space for that volume, and a quota, which limits how much it can allocate. Decide whether either boundary is needed before creating the volume. Avoid reserving space merely to make the display resemble a partitioned disk.

In Disk Utility, select an existing APFS volume in the intended container, use Add Volume, enter a recognisable name and choose the required APFS format. Review any Size Options, then add the volume. Confirm the external device identity before proceeding.

Verify the new location

After creation, check that the original volume and its files remain accessible. Put a harmless test file on the new volume, eject the device normally and reconnect it. Confirm which volume contains that file and that its name is unambiguous in Finder.

Update project instructions and backup coverage deliberately. A second volume on the same device remains exposed to loss of that device, regardless of its reserve or quota.

Keep Erase and Delete outside this addition procedure. Apple distinguishes erasing a volume’s data from deleting the volume itself; both are destructive to its contents. If the layout is not what you intended, pause with the verified backup intact rather than trying several destructive controls to tidy it up.

References: Apple: APFS volumes.