Nothing.
It’s not supported by vs 2017. In fact the current version of blazor, which you should be using, is only supported by vs 2022.
You can use the dotnet command line to create a blazor project and use vs 2017 as a text editor, but you will not be able to debug. The project probably will load either.
In short, if you want to work with blazor, you should install a version of vs 2022 or use visual studio code.