In my fleet of older Macs, I have a Late 2013 27" iMac fitted with a 3 TB Fusion Drive running macOS 10.15.7 Catalina. I was using Boot Camp to install Windows 10 Pro, when the Windows installer failed after copying Windows files to the Boot Camp partition. The Mac was then unable to boot into Windows.
I rebooted into macOS and used the Boot Camp Assistant to remove the Windows 10 installation and partition. After having cleared the PRAM and reset the SMC, I was going to try again, when I noticed that the drive was showing as 2.1 TB, not 3 TB. I rebooted into Recovery Mode and checked the drives using Disk Utilities. Everything seemed to check out.
I opened the Terminal and ran
diskutil list, which revealed the first three disks in the system (normal) plus
/dev/disk24 (all of which are disk images with varying sizes, but no type).
Exited the Terminal and opened the Disk Utility, then selected the
Macintosh HD volume, which did show the second image - 2.1 TB. Opened the Partition tab which did show a large amount of free space, but the sum of the free space and the macOS partitions is nearly 4 TB on a 3 TB drive!
How can I recover the free space? When I try to use
diskutil apfs resizeContainer to expand the macOS container
disk3 to occupy the free space, the command fails, because the combined space is larger than the media.