sudo do-release-upgrade -d

Kodi-specific: keep pam config, keep security/limits config, resolved.conf blacklist.conf /etc/sysctl.conf openssh server conf unattended upgrades mysqld.conf apticron

remove unnecessary locales

list available locales:
localedef --list-archive
locale -a

then remove all BUT THE ONES LISTED:

sudo locale-gen --purge <locales YOU WANT TO KEEP> en_GB.utf8 en_US.utf8

sudo apt-get install localepurge

After that, you could reboot or try to run . /etc/default/locale.

To reconfigure this, simply enter the following in terminal:

sudo dpkg-reconfigure localepurge

reinstate ppas after upgrade by uncommenting sources https://askubuntu.com/questions/111645/whats-the-best-way-to-re-enable-ppas-repos-after-an-upgrade

for f in /etc/apt/sources.list.d/*.list; do sudo sed -i 's/bionic/focal/g' $f; sudo sed -i 's/^# \(.*\) # disabled on upgrade to.*/\1/g' $f;done

Remove snap/lxd:

sudo apt autoremove --purge snapd gnome-software-plugin-snap