I wrote a similar answer here
To do this, first remove any lines with
Second we are going to tell apt to allow downgrades. That means pinning
focal-security with priorities higher than 1000. Create
/etc/apt/preferences.d/focal with this content:
Pin: release n=focal
Pin: release n=focal-updates
Pin: release n=focal-security
If you don't use
focal-security then skip those sections.
Third, run the following:
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt --fix-broken install
sudo apt autoremove
and keep rotating between those commands until everything is stable.
Alternatively, you can just delete
focal-proposed. Those packages will eventually migrate to
focal-updates when they pass their test and you'll be in sync again.
With your small delta,
--fix-broken install and
autoremove probably won't be neccessary but
apt will tell you when you read the output of the previous commands.
To anyone else who comes accross this post: Downgrading is not supported. Any downgrade of significant size is likely to fail. This is a pretty trivial case, but going from
bionic would probably be a disaster and leave you with a broken system.