Following a do-release-upgrade, your third-party or private repositories (such as PPAs) may be disabled. This can stop a package being updated because it can no longer find the dependencies it needs, and/or old packages conflict with newer packages.
Have a look through your .list files, usually in /etc/apt/sources.list.d, to see what needs to be re-enabled.
Then run apt update and try again.
This is happened to me after a do-release-upgrade on a Google VM.