How do I fix macOS Sequoia update issue on my iMac?

OP wrote " still running 15.1.1 " released Nov 19, 2024 >> On April 10. 2025

What follows is perhaps a longer way to achieving the update and eventually reaching Sequoia 15.4

As the computer is so far behind in updates

It maybe necessary to update to say Sequoia 15.2 >> First

If you currently have a Full Version of Sequoia in the applications folder >> Delete it and empty the Trash ( Bin )

In the Terminal application, copy and past the below command

softwareupdate --fetch-full-installer --full-installer-version 15.2

This will manually download the Full Version of Sequoia 15.2 - About 12 - 14 GB in size

If successful it will create a new application called " Install Sequoia app " in the Applications folder

When ready, Launch it like another application

Follow the prompts

Thank you for obliging us and posting the Etrecheck Report

Indeed, the computer is stuck on Sequoia 15.1.1 and for good reason

Antivirus software: Sophos

Contact the Developer of this useless software developer for the Specific Instructions to Total Remove this software and their System Extensions

The other school of thought when it comes to third party security software which is heavy handed and effective

Start Over from scratch, for Apple Silicon computer >> Use Disk Utility to erase a Mac with Apple silicon.

If going this route - it is suggest Not using Startup Assist to migrate everything back.

This will probably Re-Introduce (Sophos ) back into the Operating System 

System Extensions:

[Running] com.sophos.endpoint.scanextension - version 10.10.3 (Sophos - installed 2025-02-19)

    Application: /Applications/Sophos/Sophos Scan.app - version 10.10.3 (Sophos - installed 2025-02-19)

    Description: Scanning Services

[Running] networkextension - version 10.10.3 (Sophos - installed 2025-02-19)

    Application: /Applications/Sophos/Sophos Network Extension.app - version 10.10.3 (Sophos - installed 2025-02-19)

  [Not Loaded] TransparentProxyTestExtension - version 10.10.3 (Sophos - installed 2025-02-19)

    Application: /Applications/Sophos/Tools/Sophos Transparent Proxy Test Tool.app - version 10.10.3 (Sophos - installed 2025-02-19)

  [Not Loaded] ContentFilterTestExtension - version 10.10.3 (Sophos - installed 2025-02-19)

    Application: /Applications/Sophos/Tools/Sophos Content Filter Test Tool.app - version 10.10.3 (Sophos - installed 2025-02-19)

How did you handle creating user(s) on the Mac after erasing and resetting the drive? Did you bring over your files and settings by running Setup Assistant or Migration Assistant? Before running the update? If you brought over anything from the previous setup, it may have included remnants of the antivirus that seems to interfere with doing updates of the MacOS. Can you post the most recent Etrecheck report? That my provide clues.

 Check status of SIP in Terminal >>  csrutil status

What does it echo back ?

Very strange experience

To skip the Q&A session, just download the Application Etrecheck directly from the Developer. 

It’s a diagnostic tool that doesn’t change your computer at all. It gives you a clear and easy-to-read list of both your hardware and software. 

You can get it for free or pay for extra features. And don’t worry, the report won’t reveal any personal information. 

Once you’re done, just copy and paste the full report using the Additional Text Icon.

Well at least that potential issue is closed

What happens with you run this terminal command

It will Only Search for Full Versions of Sequoia

 softwareupdate --list-full-installers

What is the output ?

525web wrote:

I have contacted apple support and been advised that this issue is a bug in the software update that several people have been experiencing. Have to wait for a new patch to come through. Now I need to rebuild all the software and data lost in the hard drive erase.

Thanks for your assistance

Etrecheck Report >> Apple M3 (m3) CPU: 8-core "

Interesting as I have a M3 machine which was updated from Sequoia 15.3.2 to Sequoia 15.4 on the day of release March 31. 2025

Absolutely no issues what so every

FYI - also updated M2 from 15.3.2 to 15.4 and also a M4 from 15.3.2 to 15.4 - Absolutely no issues

525web wrote:

That's the way I did the delete.

Have since been advised by apple support that it is a bug in there update software and will have too wait for a fix.

Thanks for your assistance

Whatever " issues " that exist for this computer

It appear to be " unique " and " localized " to this machine / computer

Suggest it be " evaluated " my the experts

Have the computer evaluated by the Professionals who have the Special Hardware Software and Expertise to diagnose the issue and offer possible solutions

Make an Appointment at the Apple Genius Bar or call 1 800 MyApple and have them evaluate the computer

Other location Call Centres 

 Contact Apple for support and service

525web wrote:

Currently running MacOS 15.1.1 and have tried various updates including 15.4 and none work.

I have tried installing from the apple store and upgrading

Have automatic upgrades turned on

Downloaded the full installer used it

Tried upgrading from the Restore Screen

Tried upgrading in safe mode

Do not get any error messages, the upgrade seems to go through the process and after the iMac restarts it is still running on 15.1.1

Anybody got any ideas

Boot to Safe Boot mode and try again running that installer

ref:Start up your Mac in safe mode - Apple Support

login in there and compare your results.

turn off any firewall if you turned it on.