How to install MATE desktop on Ubuntu 20.04 Focal Fossa Linux - LinuxConfig.org

The objective is to install MATE desktop as an alternative desktop environment on Ubuntu 20.04 Focal Fossa Desktop/Server Linux.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-install-mate-desktop-on-ubuntu-20-04-focal-fossa-linux