Hi,
Please follow the instruction on this website and make sure all required extensions are installed: https://code.visualstudio.com/docs/other/unity
If the issue persists, please check the console of VS Code (not Unity!). If the .NET Framework 4.7.1 (Developer Pack) is mentioned there, download and install it from the official Microsoft website. Here is the link: https://dotnet.microsoft.com/download/dotnet-framework/net471
On a Mac, install the latest MONO Framework.
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