Compiler and library support for concepts is now available in Visual Studio 2019.

C++20 Concepts Are Here in Visual Studio 2019 version 16.3

by Xiang Fan

From the article:

C++20 Concepts are now supported for the first time in Visual Studio 2019 version 16.3 Preview 2. This includes both the compiler and standard library support.

First, we’re debuting the feature via /std:c++latest mode and once we have all C++20 features implemented across all Visual Studio products (compiler, library, IntelliSense, build system, debugger, etc.), we’ll provide them through a new /std:c++20 mode.