Netboot images are deprecated (not available at all for 20.10+) so debootstrap utility is used instead. I will install
minimal Plasma desktop and enable OEM mode. Then I can create my user account from within OEM session.
It seems like Chromium DEB is no longer updated, which is a huge security risk (v87 in repos, v89 upstream). "Sources list from 18.04" section is now removed, it is recommended to use Flatpak instead.