Intel based Mac Mini (2018) Sequoia 15.3.2 update failed

My Mac mini (2018) is still supported, say Apple. But I seem to have reached a crossroads with it. You see, it won't update to macOS Sequioia 15.3.2 no matter what I try, and I have tried quite hard - As Apple continues to enhance its software offerings, compatibility issues seem to be increasing. I wonder if its a sign that it is time to depart the Intel Mac owners club for good and lose my last liferaft to x86 virtualisation on macOS? Thats quite a big call for me to make as I have a few virtual machines that I do really still need. But I have one faithful old Xserve 3,1 which could be able to run them still. So this isn't really a howto post more a lament for Intel macOS and perhaps the start of a long goodbye to it. This post investigates the specifics of these installation failures and outlines potential troubleshooting steps.

TL:DR The macOS Sequoia 15.3.2 update, while introducing crucial security patches, is not installing smoothly for this Mac Mini 2018 Intel user. Comprehensive troubleshooting steps which normally alleviate common issues don't seem to be working for me so far. In the end I had to completely erase it and revert to macOS Sonoma. So, I'm done with this Mac Mini and its off to Computer Exchange...

Understanding the macOS Sequoia 15.3.2 update

The macOS Sequoia 15.3.2 update was released with several enhancements aimed primarily at supporting the latest MacBook Air models featuring the M4 chip and the M3/M4 Mac Studio ranges. Complementing the introduction of advanced hardware, Apple has also patched notable security vulnerabilities, including a fix for a serious flaw within the Safari WebKit framework. This flaw could have permitted maliciously crafted web content to escape its designated sandbox, presenting a significant threat to user data. As sophisticated cyber threats continue to evolve, such updates should not be overlooked.

Software Update Available

Ok, lets try Software Uodate again. Step-by-step, to install this fussy Sequoia update. 

Accepted the licence agreement.

macOS doesn't seem to like this update. It says "Failed to prepare the softare update. Please try again. An error occured while downloading the selected updates. Please check your internet connection and try again". This is a perplexing message as it could mean a zillion things.

Download the macOS installer from Apple

Apple make it reasonably easy to download the install image for whatever verison of macOS is needed, subject so some constraints about the machine you are downloading from. So follow the instructions in How to download and install macOS and you'll be let to links to macOS in the App Store.

• Sequoia 15

• Sonoma 14

• Ventura 13

• Monterey 12

• Big Sur 11

• Catalina 10.15

• Mojave 10.14

• High Sierra 10.13

Click the Get button in the App Store to begin downloading. Software Update might open and ask you to download from there.

After downloading to your Applications folder, the installer opens automatically. Follow the onscreen installation instructions. Or quit without installing to leave the installer in your Applications folder for later use. 

Installer is damaged

Disk First Aid

Trying Disk First Aid

First Aid ran successfully. It was a hunch that this might be an issue. It isn't. 

Create a bootable installer for macOS

Error: The bless of the installer disk failed

Following Apple's support instructions for creating a a bootable installer for macOS failed, and it appears I am not alone. Plenty of similar reports out there. One wonders what to do next.

% sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/Install\ macOS\ Sequoia
Password:
Ready to start.
To continue we need to erase the volume at /Volumes/Install macOS Sequoia.
If you wish to continue type (Y) then press return: Y
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying essential files...
Copying the macOS RecoveryOS...
Couldn't extract BaseSystem to path: /Volumes/Install macOS Sequoia/BaseSystem
The bless of the installer disk failed.

SilentKnight

I rebooted and loaded the wonderfully detailed tool SilentKnight. It reports no issues other than a warning over XPR which can be ignored for now and that Software Update found the following new or updated software: 

• Label: macOS Sequoia 15.3.2-24D81
• Title: macOS Sequoia 15.3.2, Version: 15.3.2, Size: 1355633KiB, Recommended: YES, Action: restart

Although not recommended for macOS I clicked 'Install all updates' and it failed again.

Used another Mac, an Apple Mac Studio

I used another Mac computer, an M1 based Mac Studio to create a boot disk - this time successfully!

% sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/Install\ macOS\ Sequoia 
Password:
Ready to start.
To continue we need to erase the volume at /Volumes/Install macOS Sequoia.
If you wish to continue type (Y) then press return: Y
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying essential files...
Copying the macOS RecoveryOS...
Making disk bootable...
Copying to disk: 0%... 10%... 20%... 30%... 40%... 50%... 60%...^[ 70%... 80%... 90%... 100%
Install media now available at "/Volumes/Install macOS Sequoia"

 I have no explanation for why this command would not work on my Intel based Mac Mini

Turn off Find My Mac.

On an Intel Mac with a T2 chip you need to disable Activation Lock. When you're done using macOS Recovery, you can enable Activation Lock again.

To disable Activation Lock, turn off Find My Mac.

macOS Sequoia USB installer

Ran the installer from this USB stick, which takes a very long time. It loaded eventually and started to install but ended up with the same error message.

This error led me to think it migh be associated with some kind of connectivity issue with Apple's servers, so I tried Internet Recovery (⌘ - Option - R) on boot.

Internet Recovery reminds me of the logo for AppleLink ( you have to be quite old to remember it )

Apples error from Internet recovery is annoyingly different and similarly non specific.

No Fix - reverted to Sonoma

I can't get this update to install. I was able to create a macOS Sonoma USB stick using the same USB stick. It installed perfectly. So I believe this to be an issue with the macOS Sequoia 15.3.2 image. I've decided to give up, and move away from Intel macOS. So I've returned the machine to out of box experience for a new owner.

Cost of ownership - Mac Mini (2018) - under a fiver a week

I bought this Mac Mini for £720 on 16 March 2023 from Computer Exchange and sold it for £201 on 21 March 2025 to computer Exchange so its cost of ownership to me was £519 over two years, thats £4.93 per week. Its been a useful insurance for me as I moved to Mac computers with Apple silicon but that time is over.

What about my Intel VM's?

Fortunately for me, VMWare decided to make "VMware Fusion and VMware Workstation more accessible than ever. Starting November 11, 2024, these powerful desktop hypervisor products will be available for free to everyone—commercial, educational, and personal users alike". - VMware Blog.

It was as simple as copying the VMware virtual machine to a Windows PC answering the question 'I moved it' see VMware Fusion and wokrstation are Free Now – Moving a Virtual Machine from Mac to PC is Easy. I had to reactivate Windows which worked using the product key from the destination Windows PC which I was able to fish out of the CMOS/BOIS memory. See Find your Windows product key.