With the release of Visual Studio 2017 Update 6 (version 15.6.x), you might have noticed that there was an update done to the New Project dialog to move the .NET Framework version selector down to the bottom below the solution name. This makes the New Project dialog cleaner and shows you which version of the .NET Framework will be used when creating your project.
The Framework selector disappears when selecting non .NET Framework projects like ASP.NET Core, UWP, etc.
Enjoy!