Refer: https://www.howtogeek.com/107368/how-to-install-the-lightweight-lxde-desktop-on-ubuntu/
$ sudo apt-get install -y lubuntu-gtk-core lubuntu-gtk-desktop
$ sudo apt-get install -y lubuntu-desktop

Technical notes, and other ideas.
Refer: https://www.howtogeek.com/107368/how-to-install-the-lightweight-lxde-desktop-on-ubuntu/
$ sudo apt-get install -y lubuntu-gtk-core lubuntu-gtk-desktop
$ sudo apt-get install -y lubuntu-desktop