Comment 2 for bug 1886357

You seem to have some python3.8 packages installed with version numbers that are greater than ones in the release to which you are trying to upgrade. This is causing the failure to calculate the upgrade so please remove them and try the upgrade again.

libpython3.8-minimal 3.8.3-1+bionic1 1
libpython3.8-stdlib 3.8.3-1+bionic1 1
python3.8 3.8.3-1+bionic1 0
python3.8-minimal 3.8.3-1+bionic1 1

Thanks and good luck!