Can't upgrade Ubuntu 18.04 to 20.04 because of "Please install all available updates for your release before upgrading" error
I've been trying to upgrade my version of Ubuntu 18.04 to 20.04. I've run all the steps from updating and upgrading both apt and apt-get, changing the settings in update manager and all of the steps described in this link. Yet I keep getting the error:
Please install all available updates for your release before upgrading.
Is there something special about trying to upgrade from 18.04 to 20.04 that's causing this error? Do I maybe need to update to 19.04 first?
EDIT: I just noticed something that might be important. When I run
sudo apt-get update I get the following notice at the end of the output:
The following packages have been kept back:
colord gimagereader python-sane sane simple-scan
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
Might that be causing the issue?