Generate a class diagram from Visual Studio

For Visual Studio 2017, 2019 and 2022

This feature is still available, but it is NOT installed by default, you have to install it separately.

1. From inside Visual Studio go to Tools -> Get Tools and Features
2. Select the Individual components tab and search for Class Designer
3. Check this Component and Install it

After finish installing this component

1. Right-click on the project and select Add -> Add New Item
   A. Search for ‘class’ word and NOW you can see Class Diagram component

Very Important Update From the Comments below

1. Right-clicking on a folder and selecting Add New Item will NOT show the Class Diagram option.
   You could right-click on a project.
2. Not every project type will support Class Diagram For example,
   Right-clicking on Class Library project will DO show Class Diagram option in the Add New Item dialog.
   
   But Right-clicking on ASP.NET project will NOT show Class Diagram option in the Add New Item dialog.