MacBook M4: APFS corruption prevents disk space reclamation

That is interesting and something I've never seen. That's certainly unallocated space!

Given everything that you've already attempted, this looks like a prime example of directory corruption.

I think the only way to fix this is to "...take off and nuke the entire site from orbit. It's the only way to be sure."

Backup your data. Then boot into recovery and erase and reformat the drive. Then reinstall macOS and finally recover your data from your backup. This is one of those times when your backup will earn its keep.

One saving grace here in your situation is that the drive is only 256 GB and your Mac is very fast, so backing up and recovering your stuff won't take long.

Edit - What was on this "secondary APFS volume" before you deleted it?

Thanks.

Now how about giving us a look at the drives as listed with the Terminal command: diskutil list

m7taha wrote:

[...]

Request: Guidance on how to repair the APFS container corruption and reclaim the unallocated 60GB of disk space on an M4 Mac without erasing and reinstalling macOS.

The startup drive cannot be repaired unless the computer is booted from another drive or in Recovery mode.

Have you tried running Disk Utility's First Aid on the drive while booted in recovery?

(It's an obvious thing, but you didn't include it in your very thorough post.)

How to repair a Mac storage device with Disk Utility - Apple Support

m7taha wrote:

The secondary volume was created intentionally to have two separate partitions. It was used for storing files separately from the main macOS volume. I deleted it thinking I will be able to merge back into the main container, which is when this problem started.

You actually created a new partition which made major changes to the drive layout. Modifying partitions is very risky and should be 100% avoided. People always realize much later that one or more partitions is too small and will almost always run into problems to fix things as you have discovered here.

While I have several posts on this forum with instructions to merge that "(free space)" back into the APFS Container, it won't do any good because of the file system issues reported by Disk Utility. This is why Disk Utility is refusing to merge it back together. Either you need to run First Aid from Recovery Mode by following the instructions in the following Apple article, or you need to erase the disk (aka the Volume Group) if the Container has errors/warnings that remain.

How to repair a Mac storage device with Disk Utility - Apple Support

Use the "If you cannot use Erase All Content & Settings" option if the Container has any unfixed errors/warnings, otherwise you can use the first option:

Erase your Mac and reset it to factory settings - Apple Support

Fortunately for you, macOS has a new option for creating new APFS volumes within the same Container as your OS installation. These new APFS volumes act a lot like partitions, but instead of making major risky changes to the drive layout (partition table), the APFS volumes share the same storage pool so you do not have to designate any sizes. You can put size restrictions on a new APFS volume if you wish, but I don't know if they can be changed later....for a simple data volume I don't think it you should put any restrictions on it. @D.I. Johnson provide a link to an Apple article about creating APFS volumes.

m7taha wrote:

The secondary volume was created intentionally to have two separate partitions. It was used for storing files separately from the main macOS volume. I deleted it thinking I will be able to merge back into the main container, which is when this problem started.

Understandable.

Something to know as you move forward is that with the new APFS drive format, partitioning a drive is no longer necessary, even for the situation you describe. Except, of course, when preparing a new drive for Mac use.

In the APFS formatted drive you can see that a container is created, and within that container are the APFS volumes. The container now manages the storage and dynamically allocates more or less space to any volume in the container that needs it or frees it. The volumes share the totality of the drive space.

Role of Apple File System - Apple Support

So, instead of repartitioning a drive, the thing to do now is simply add and/or delete APFS volumes to the container. They behave more or less like partitions the old formats used. It's much faster and safer to add or delete a volume than to repartition a drive. When you delete an APFS volume, the storage that volume has been using is automatically dumped back into the pool of storage managed by the container and made available to any other APFS volumes as they require.

Add, delete, or erase APFS volumes in Disk Utility on Mac - Apple Support

May we get a look at the situation as seen from Disk Utility's display, please?