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