vscode on linux: omnisharp "problems" with aspnetcore: "The type or namespace name 'Authorization' does not exist in the namespace"

I have a project that works in VSCode on Windows, but when loading it on Linux it yields several "Problems":

The type or namespace name 'Authorization' does not exist in the namespace 'Microsoft.AspNetCore' (are you missing an assembly reference?) [money, money, money, money]

And several others.

Do I need to configure VSCode to find these dlls somehow?