"Failed to prepare the software update" when trying to update from Sonoma 14.4.1 to 14.5

Ok, I have been able to fix the issue. Note that I had the exact same error messages as you and I also tried all what you tried and similarly failed (getting stuck also at 65%, etc). The fix was to enter into DFU or Device Firmware Upgrade mode and revive the Mac (the error code indicated something was wrong at a deeper lever). For this you need a second Mac running macOS 14 (if you do not want to install a special software that I believe is needed for earlier version of macOS) with a USB-C to USB-C cable (I used the power supply cable of the laptop). Explanations are here How to revive or restore Mac firmware - Apple Support

Reviving installed some 700 MB of firmware updates to the problematic iMac Pro (using the internet connection of the MacBook Pro and with the two Macs connected). Once the iMac Pro had been revived (and not restored, this is important as restoring erases everything, while reviving does not erase anything), I was able to update to 14.5. Hope this helps!

The error message I receive upgrading my Intel based mac mini (2020) appears to indicate a problem with the macOS installer script: the installer is attempting to expand UpdateBrain.zip on a read-only volume (a disk image) and then complaining about no space left. BridgeOS should be updated automatically during upgrade, but it is failing and consequently requiring the DFU workaround. Will Apple ever fix newer macOS installers to properly upgrade the bridgeOS on Intel based macs? I don't have another Apple running Sonoma to fix using DFU mode, hoping for Apple to fix the installer... Is waiting for installer fix a viable option? I would like to install Monterey, is it reasonable to expect they will fix that installer in a newer release?

Thee3 wrote:

• Things I already tried:

Shutdown / restart the Mac

• Boot into safe mode and then try to update

• Disk check "First Aid"

• Manually update using terminal, which yields this error message:

sudo softwareupdate -i -a

Software Update Tool

Finding available software

Downloading macOS Sonoma 14.5

Downloading: 100.00%

Failed to download & prepare update: Error Domain=SUOSUErrorDomain Code=201 "Failed to prepare the software update. Please try again." UserInfo={NSLocalizedRecoverySuggestion=An error occurred while downloading the selected updates. Please check your internet connection and try again., NSLocalizedDescription=Failed to prepare the software update. Please try again., NSUnderlyingError=0x600003f50000 {Error Domain=SUMacControllerError Code=7740 "[SUMacControllerErrorPrepareFailed=7740] Failed to perform Prepare operation: [MobileSoftwareUpdateErrorDomain(MSU):MSU_ERR_BRIDGEOS_PREPARE_FAILURE(45)_1_BOSErrorDomain:205_2_BridgeOSSoftwareUpdateError:19]" UserInfo={NSLocalizedDescription=Failed to prepare the software update. Please try again., SUMacControllerErrorIndicationsMask=0, NSDebugDescription=[SUMacControllerErrorPrepareFailed=7740] Failed to perform Prepare operation: [MobileSoftwareUpdateErrorDomain(MSU):MSU_ERR_BRIDGEOS_PREPARE_FAILURE(45)_1_BOSErrorDomain:205_2_BridgeOSSoftwareUpdateError:19], NSUnderlyingError=0x600003f52370 {Error Domain=MobileSoftwareUpdateErrorDomain Code=45 "bridgeOS prepare failed" UserInfo={NSUnderlyingError=0x600003f52400 {Error Domain=BOSErrorDomain Code=205 "An error occurred during prepare." UserInfo=0x600002451280 (not displayed)}, NSLocalizedDescription=bridgeOS prepare failed, target_update=23F79}}}}}

The download gets stuck at 65% and it stays there for about 5 minutes and then this error message comes.

My internet connection is fine and everything works well except this update.

Spec:

Intel iMac Retina 5K, 27-inch, 2020

Any ideas how to solve this problem? Thanks.

If you have an issue alternatively you can try —

softwareupdate --fetch-full-installer --full-installer-version 14.5

if it is a server issue I would simple try again later hour/day...

I see some server issues—even though software is not list as one of them, Apple does not like to flag issues unless it is wide spread... ref: Apple - Support - System Status

Thee3 wrote:

I'm still having the same problem. I have successfully updated my 2019 MacBook Pro to Sonoma 14.5 so it's not a server or a connection issue. The update is getting downloaded just fine, but the process of updating fails. Anyone has any suggestions?

Did you try booting into SafeBoot Mode and launch the installer...

A SafeBoot Use safe mode on your Mac - Apple Support will sort many anomalies; Login and test.

Known issues on the macOS—

third party apps that are Cleaners/Optimizers/VPN/Anti-Virus, the recommendation would be to uninstall if applicable.

Thee3 wrote:

Could be a server issue, but I have tried it yesterday and multiple times today with no luck.

What does the command you provided do? Thanks

It downloads the the full installer < full-installer-version 14.5 >

When complete it will be sitting in your Applications folder "Install macOS Sonoma.app"

When you are ready you launch it from there like an other application. It will remove itself when the update is complete.

I have the exact same issue with a 2017 iMac Pro. Impossible to update. Have you been able to find a solution?

Turning off all of MS Defender options finally let me update. Seems the real time and cloud delivered options prevented the update to finalize.

Easy option if it works for you!