Unable to write to last block of the device : (69760)

A better alternative to writing zeroes to an SSD is to reset the SSD to factory defaults using SSD's built-in hardware secure erase feature. It resets all blocks on the SSD with minimal wear and it also resets other aspects of the SSD to factory defaults which can also fix some weird SSD issues. However, not all Apple SSDs support this feature and it does require the use of a Linux utility.

Parted Magic is a customized Linux utility boot disk which has this ability to reset an SSD to factory defaults with an easy to use app. The last free version of Parted Magic can be downloaded from the Major Geeks' link here. Here is information about the procedure using the newer paid version.

https://partedmagic.com/secure-erase/

While the interface is a bit different, the basics are the same. If the computer is using an NVMe SSD, then the paid version is most likely necessary.

Create a bootable Parted Magic USB drive using Etcher (Mac/Windows/Linux). Option Boot the USB drive and select the orange icon labeled "EFI". There should be an icon on the Parted Magic desktop for erasing drives. Within the app you will need to select the "ATA Secure Erase" option as it is the only option that will reset the SSD to factory defaults. All other options will just cause undue wear on the SSD by writing zeroes to the drive.

The "ATA Secure Erase" option will require you to sleep & wake the computer followed by supplying a temporary password to enable the security feature necessary for the ATA Secure Erase. Keep it simple with something like "abc" since you may need this password to unlock the drive if the erase fails or is interupted. If you forget this password the drive may become permanently locked if the procedure does not complete successfully. Normally the "ATA Secure Erase" will take somewhere between 30 seconds to several minutes (maybe even up to five minutes for some SSDs).

Parted Magic also contains other utilities which can access the SSD's SMART features to check its health and even run the SSD's internal self diagnostics (again not all Apple SSDs have these features).

Here's another article on fixing this problem: How to fix deep formatting problems with OS X drives | MacIssues. Not sure if you get the SSD fixed. The article seems to be for fixing an external drive.

I know of one possible method to fix an SSD. It involves a one-pass secure erase that writes zeroes to the entire disk. Unfortunately, doing this on an SSD will affect the life of the SSD which is affected by how many write operations the SSD can perform before failing. This particular solution will affect that life but I don't think the life of the SSD is shortened dramatically. You can us Disk Utility or the Terminal. For the Terminal enter:

zeroDisk force /dev/disk0

Press RETURN. Wait for the process to be completed. There should be some indicator of success.

If you use Disk Utility, then select the disk entry (Apple SSD SM0128G) and click on the Erase button in the toolbar. From the dropdown panel click on the Security Options button. Use the indicator to select the number of passes. One-pass is all that is needed. Note that the indicator is normally set to 0 passes. So you must set whichever is the next setting. That is the minimum number of passes. Click on the OK button then click on the Erase button.

As with the Terminal process this takes a lot of time, so be patient and wait until completion.

Both of these methods are similar to that used in the linked article. That is, they both write data to the entire disk. When finished you will have to re-partition and reformat the disk as you would for normal use. If you are using Mojave or Catalina, then be sure to choose APFS as the Format Type.

I hope you find some success because I'm at the end of what I know about trying to fix this error. If you are still unable to fix the disk, then you will need to take it to your local Apple Store when they re-open (Mar. 27.)

See the following: Fixing an Unable to Write to the Last Block of the Device Error.