This issue is tracked here: https://github.com/aspnet/Tooling/issues/479
Reinstalling Visual Studio to a different npm path will most likely not make a difference - Visual Studio still seems to interpret the dependency on a package that is not supported on Windows as a problem.
This is a problem only with the IDE. You can still create and run without resolving this problem.
But if you prefer to get rid of the not installed indicator, identify and remove the corrupted package, then manually delete the node_modules folder and save package.json .
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