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

Remove legacy xorg drivers, keep only intel

sudo apt-get purge xserver-xorg-video-vmware xserver-xorg-video-radeon xserver-xorg-video-qxl xserver-xorg-video-nouveau xserver-xorg-video-intel-hwe-18.04 xserver-xorg-video-ati xserver-xorg-video-amdgpu xserver-xorg-legacy-hwe-18.04 xserver-xorg-legacy xserver-xorg-video-all xserver-xorg-hwe-18.04 xserver-xorg-core-hwe-18.04 xserver-xorg-video-fbdev xserver-xorg-video-vesa xserver-xorg-video-intel

remove edid firmware patch and update initramfs and grub

vi /etc/default/grub

set

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

sudo update-grub

sudo apt-get install xserver-xorg-legacy xserver-xorg-video-intel

#set to everyone

sudo dpkg-reconfigure xserver-xorg-legacy

sudo vi /etc/X11/Xwrapper.config

add

needs_root_rights=yes

Adjust Alsa options:

sudo vi /etc/modprobe.d/alsa-base.conf

#options snd-hda-intel enable_msi=1 bdl_pos_adj=1,48
options snd-hda-intel power_save=0 power_save_controller=N

OR

sudo echo -e '\n# Disable snd-hda-intel power saving\noptions snd-hda-intel power_save=0 power_save_controller=N\n' >> /etc/modprobe.d/alsa-base.conf

Reinstall virtualbox (if required):

sudo apt install virtualbox