SSD drive partition showing as FFFF on my MacBook Pro 2010

Solution 1:

If you are able to repair you drive, then you will need to be running at least Sierra in order to mount the macOS partition on the SSD via USB.

Below are two possible solutions.

Using a Third Party Tool

Since you already have the SSD connected as disk2 in a USB port, a simple solution would be to download and use gdisk.

The current gdisk installer is named gdisk-1.0.4.pkg. I will assume this will download to your Downloads folder. Before opening this file to install gdisk, you may need to remove the quarantine by executing the command given below.

xattr -d com.apple.quarantine ~/Downloads/gdisk-1.0.4.pkg

Once gdisk is installed you would need to enter the following command.

gdisk /dev/disk2

The gdisk command is interactive. What you need to enter into gdisk is given below. This input is only valid if you use version 1.0.4 or a newer version of gdisk.

t
2
AF0A
w
y

Below is an example of what you should see.

GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): t
Partition number (1-3): 2
Current type is 'Unknown'
Hex code or GUID (L to show codes, Enter = AF00): AF0A
Changed type of partition to 'Apple APFS'

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/disk2.
Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Warning: The kernel may continue to use old or deleted partitions.
You should reboot or remove the drive.
The operation has completed successfully.

Without Using Any Third Party Tools

An answer Klanomath might have posted would include entering the commands given below.

diskutil unmountdisk disk2
gpt remove -i 2 /dev/disk2
fdisk -e /dev/disk2
e 2
0
q
y
diskutil unmountdisk disk2
gpt add -i 2 -b 409640 -s 781512664 -t 7C3457EF-0000-11AA-AA11-00306543ECAC /dev/disk2 
fdisk -e /dev/disk2
e 2
FF
n
409640
781512664
q
y

Basically you are performing the following steps.

1. Removing the macOS partition from the GUID partition table (GPT).
2. Removing the macOS partition from the Master Boot Record (MBR) partition table.
3. Adding the macOS partition back into the GUID partition table (GPT) using the correct partition type.
4. Adding the macOS partition back into the Master Boot Record (MBR) partition table. (This is an undo of step 2.)

Final Note

Your APFS partition is about 50 MB larger than the APFS container. While this will not present a problem, I mention this fact for other readers who may be more observant.