Failed to personalise the software update. Please try again.

There are factors:

Some which are beyond your control and those with are totally under your control

Empty Space or Lack of Empty Space on the drive

Software on the computer interfering with the download process including AntiVirus Software

Notation: Disabling the AV Software may or may not solve the issue.

Removal of the AV Software may increase the chances of the download to perform as expected.

Running behind a VPN which may increase Packet losses or corruption of the download 

Turn off any Third Party Two Way Firewall and try again 

Best Results are via Ethernet Cable to Router

Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal 

Try Again using the Software Update Applet in System Preferences / Setting 

Worst case - Restart in Recovery Mode and choose Reinstall macOS. 

This in theory will pull the latest version of macOS this computer qualifies to run 

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.

Consider this Third Party Software to find and possible remove all elements of Wireshark

https://findanyfile.app/

1 - Elements  of Wireshark are installed 

" org.wireshark.ChmodBPF.plist (Wireshark Foundation - installed 2025-01-17)

    Executable: /Library/Application Support/Wireshark/ChmodBPF/ChmodBPF "

2 - disk0 - APPLE SSD AP0512Z 500.28 GB (Solid State - TRIM: Yes) 

Size: 494.38 GB

      Free: 246.81 GB

      Available: 338.67 GB

Free Space versus Available Space 

From another contributor @etresoft regarding Free Space and Available Space 

Free vs available disk space huge differe… - Apple Community

Quote >>  “ The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary. The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder. When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule.

Certain tools will allow you to force the issue and manually clean up some of this storage and manually delete local snapshots. But that is only temporary. "  << End Quote 

An aside

Have upGraded 2 M-Class computer from Sonoma macOS 14 to Sequoia macOS 15 without issues

Have upDated 1 M4 machine which started with Sequoia 15.0 " Out of the Box " to every version up to and including Sequoia 15.3.2 also with out any issues

A very Quick Look

org.wireshark.