Microsoft abandoned MonoDevelop GitHub repository earlier this year, 

• .NET 5 provides two options of runtimes for users: the high-performance CoreCLR (for server and desktop applications), and the lightweight Mono (for mobile and WebAssembly). 

Add Mono to the dotnet\runtime repository 

The IL Linker is a tool one can use to only ship the minimal possible IL code and metadata that a set of programs might require to run as opposed to the full libraries

Using Mono for running .NET Core tests on Linux