Big problem after erase and clean install of Big Sur!

The correct procedure would have been to erase the whole drive, and not just the volumes.

Fortunately, this is easy to fix!

Control-click the BOTTOM "Data" volume - that is the one that says "Mount Point: /Volumes/Macintosh HD - Data" and choose

"Delete APFS Volume".

Ian R. Brown wrote:

Thanks Tom and Luis.

I started out with Tom's suggestion by selecting the lower Mac HD Data and clicked on "erase".

This removed the data but the volume remained.

I then followed your advice Luis, which only appeared afterwards and that got rid of the unnecessary volume.

I originally wanted to erase the whole drive but only the 2 options in my first screen shot were visible.

How should I have done it? I have never had this problem before.

As Tom said before, you'd need to first select View->Show All Devices, then erase the whole drive:

Use View>Show All Devices. You should see the container that holds the volumes. Select each volume and use - to remove the volume, then erase the container. I can't show you a screenshot at the moment unfortunately.

Not erase. Click on - minus.