Here’s a helpful, straightforward guide to understanding – with a note about the “2021” reference.
Think of the .NET Desktop Runtime as a .Apps are often written in languages like C# or VB.NET. Your computer’s processor doesn't speak those languages natively. The runtime sits between the app and your hardware, "running" the code so the application functions correctly. Specifically, the Desktop Runtime allows you to run: microsoftnet desktop runtime 80 x64 2021