Best practice is to choose “Windows Forms App” for new development.
Visual Studio gives developers the option of creating projects based on .NET Framework or .NET Core. Both have been superseded with the release of .NET 5. Developers still have the option to create projects with the .NET Framework, which is why there are two project types.
.NET Framework is older than .NET Core, and runs on Windows only. .NET Core was created to be cross-platform, and originally did not support Windows desktop apps. They had separate releases through .NET Framework 4.8 and .NET Core 3.1.
When .NET Core 3.0 was released, Microsoft began recommending that new applications, regardless of what type, be developed with .NET Core. Microsoft also announced that there would be no further major update to the .NET Framework:
With the .NET Core 3.0 release in September 2019 we think that all new .NET applications should be based on .NET Core. The primary application types from .NET Framework are supported, and where we did not port something over there is a recommended modern replacement. All future investment in .NET will be in .NET Core.
.NET Framework 4.8 will be the last major version of .NET Framework.
Source: .NET Core is the Future of .NET
Further, .NET 5 is the successor of .NET Core and .NET Framework. From now on, there’s just .NET:
There will be just one .NET going forward, and you will be able to use it to target Windows, Linux, macOS, iOS, Android, tvOS, watchOS and WebAssembly and more.
Source: Introducing .NET 5.