ROSをインストールしてたUbuntu 18.04を20.04にアップグレードする

sudo apt update
sudo apt upgrade
sudo apt install update-manager-core

$ cat /etc/update-manager/release-upgrades
# Default behavior for the release upgrader.

[DEFAULT]
# Default prompting and upgrade behavior, valid options:
#
#  never  - Never check for, or allow upgrading to, a new release.
#  normal - Check to see if a new release is available.  If more than one new
#           release is found, the release upgrader will attempt to upgrade to
#           the supported release that immediately succeeds the
#           currently-running release.
#  lts    - Check to see if a new LTS release is available.  The upgrader
#           will attempt to upgrade to the first LTS release available after
#           the currently-running one.  Note that if this option is used and
#           the currently-running release is not itself an LTS release the
#           upgrader will assume prompt was meant to be normal.
Prompt=lts

sudo apt remove "ros-*"
sudo apt dist-upgrade
sudo apt autoremove

sudo do-release-upgrade

$ grep "focal" /etc/apt/sources.list.d/*
/etc/apt/sources.list.d/danielrichter2007-ubuntu-grub-customizer-bionic.list:# deb http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/docker.list: deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable # disabled on upgrade to focal
/etc/apt/sources.list.d/graphics-drivers-ubuntu-ppa-bionic.list:# deb http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/gyazo_gyazo-for-linux.list:# deb https://packagecloud.io/gyazo/gyazo-for-linux/ubuntu/ focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/gyazo_gyazo-for-linux.list:# deb-src https://packagecloud.io/gyazo/gyazo-for-linux/ubuntu/ focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/nvidia-docker.list:# deb https://nvidia.github.io/libnvidia-container/stable/ubuntu18.04/$(ARCH) / # disabled on upgrade to focal
/etc/apt/sources.list.d/nvidia-docker.list:# deb https://nvidia.github.io/nvidia-container-runtime/ubuntu18.04/$(ARCH) / # disabled on upgrade to focal
/etc/apt/sources.list.d/nvidia-docker.list:# deb https://nvidia.github.io/nvidia-docker/ubuntu18.04/$(ARCH) / # disabled on upgrade to focal
/etc/apt/sources.list.d/ubuntu-ja.list:# deb http://archive.ubuntulinux.jp/ubuntu focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/ubuntu-ja.list:# deb-src http://archive.ubuntulinux.jp/ubuntu focal main # disabled on upgrade to focal
/etc/apt/sources.list.d/ubuntu-ja.list:# deb http://archive.ubuntulinux.jp/ubuntu-ja-non-free focal multiverse # disabled on upgrade to focal
/etc/apt/sources.list.d/ubuntu-ja.list:# deb-src http://archive.ubuntulinux.jp/ubuntu-ja-non-free focal multiverse # disabled on upgrade to focal
/etc/apt/sources.list.d/vscode.list:# deb [arch=amd64,arm64,armhf] http://packages.microsoft.com/repos/code stable main # disabled on upgrade to focal

deb [arch=amd64] http://packages.ros.org/ros2/ubuntu bionic main
deb [arch=amd64 signed-by=/usr/share/keyrings/ros-archive-keyring.gpg] http://packages.ros.org/ros2/ubuntu bionic main

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This can be caused by:
 * Upgrading to a pre-release version of Ubuntu
 * Running the current pre-release version of Ubuntu
 * Unofficial software packages not provided by Ubuntu

If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.

$ grep Broken /var/log/dist-upgrade/apt.log