How do I exclude files/folders from a .NET Core/Standard project?

There are also a few things you can do in the csproj files to make sure the files aren't picked up:

1) Make sure none of the globbing patterns that look for "project items" pick up the files:

<PropertyGroup>
  <DefaultItemExcludes>$(DefaultItemExcludes);your_nonproj.file;a\**\*.pattern</DefaultItemExcludes>
</PropertyGroup>

2) Remove items explicitly:

<ItemGroup>
  <None Remove="hidden.file" />
  <Content Remove="wwwroot\lib\**\*" />
</ItemGroup>

Note that, on large directories (number of files), using DefaultItemExcludes with the folder\** pattern is a lot faster since msbuild will skip walking the directory entirely. Using a remove for this will still let msbuild spend quite some time discovering files.

Just to be complete, if you're using ItemGroup to exclude folder, then:

<ItemGroup>
  <Content Remove="excluded_folder\**" />
  <Compile Remove="excluded_folder\**" />
  <EmbeddedResource Remove="excluded_folder\**" />
  <None Remove="excluded_folder\**" />
</ItemGroup>

Because, I had an angular project with the node_modules folder which had very long paths and VS kept throwing exceptions. And using <Content Remove="node_modules\**\*" /> didn't work.

Open the project in Visual Studio, and right click the files and folders in Solution Explorer. Choose Exclude from Project.

That's exactly what you do for projects targeting .NET Framework.