Upgrade 22.04 to 24.04 problem

I've tried this various times since it first started prompting me but always the same result despite doing all the apt update, autoremove and upgrade stuff mention elsewhere.

It always fails at the end of setting new software channels file 233 of 234 and gives this unhelpful messageThe network connection is absolutely fine both before, during up to the fail point, and after.

Surely I don't have to start from scratch with a fresh install and have to reinstall all apps to go from 22.04 to 24.04.

Any ideas or suggestions (or where I can look for more clues as to why it fails)