Install mono on Ubuntu

Run the following commands to install mono

sudo apt update

sudo apt install dirmngr gnupg apt-transport-https ca-certificates software-properties-common

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 
3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF

sudo apt-add-repository 'deb https://download.mono-project.com/repo/ubuntu stable-focal main'

sudo apt install mono-complete

Progress will look like this

Confirm if the package is installed by running the following command:

apt -qq list mono-complete

The output should look like this:

mono-complete/stable-focal,now 6.12.0.122-0xamarin1+ubuntu2004b1 amd64 [installed]