Today I tried upgrading from Kubuntu 22.04 to 23.10 using the following command:  

sudo do-release-upgrade

It went through the motions then came up with the following error message:

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by: * Unofficial software packages not provided by Ubuntu Please use the tool 'ppa-purge' from the ppa-purge package to remove software from a Launchpad PPA and try the upgrade again.

I read up on ppa-purge and  gathered that it will uninstall a program that was installed via a purged ppa if there isn't an earlier version in one of the official Ubuntu repositories. 

How am I supposed to know what ppa to purge?  Am I supposed to go through them one at a time until the upgrade is successful?  I imagine a horror story of purging a bunch of programs, not remembering what they are then finding out over the next few weeks as I try to run a program only to find it's not there and figuring out how to reinstall it again.

Or is there something I'm missing?

thanks