Vitux published a tutorial about installing Mono on Ubuntu 20.04.
How to Install Mono on Ubuntu 20.04
Mono is the OpenSource implementation of the Microsoft .NET software stack. It is based on ECMA/ISO standards and implements the C# programming language and the Common Language Runtime. To find out more about Mono, have a look at the Mono project website.
In this article, I will show you how to install the Mono Stack and c# language runtime on Ubuntu Linux. We will be using Ubuntu 20.04 system here.