The update worked without issue on my iMac 11,2, a 2010 iMac.
That indicates it is not the update, but rather something on your computer that is failing the update.
Before doing any updates, it is a good idea to check the health of the drive with DriveDX:
https://binaryfruit.com/drivedx
Then if it is healthy, run Malwarebytes & Etrecheck to make sure no malware is installed.
Avast is good as well.
If Etrecheck still find stuff after Avast and Malwarebytes that could be problematic like MacKeeper, Advanced Mac Cleaner, or any Cleanup application, remove all of those with Devon Technologies EasyFind and reboot, and make sure Etrecheck does not find anything bad.
I charge $150 for those service and will do it remotely, if you need help.
Only once you are backed up, have no malware on the computer, should you perform updates.
And only when you need software only available on that update or something newer.