Update the list of packages

 sudo apt-get update

Install pre-requisite packages.

 sudo apt-get install -y wget apt-transport-https software-properties-common

Download the Microsoft repository GPG keys

 wget -q https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb

Register the Microsoft repository GPG keys

 sudo dpkg -i packages-microsoft-prod.deb

Update the list of packages after we added packages.microsoft.com

 sudo apt-get update

Install PowerShell

 sudo apt-get install -y powershell