iMac model A2116 does not upgrade from Mojave (macOS 10.14.6) to MacOS Ventura."

Follow previous advise - First

Only as a Fall Back position on this issue

The message might say that an error occurred while downloading, preparing, or installing, or that the installer is damaged or could not be verified.

Notation - Is the computer running the latest version of Mojave 10.14.6 with all the Security Updates available ?

Attempting to upGrade from this far back in the macOS Eco-System with a computer not running the latest of Mojave can have unintended consequences including what is occurring now.

Use the About the Mac from Top left is screen.

Look for the Build Number of Mojave

The follow this link and scroll to bottom of the page

Compare your Build Number with the Newest Build Number

https://en.wikipedia.org/wiki/MacOS_Mojave

Try again while in Safe Mode.

Use safe mode on your Mac - Apple Support