How can we exclude certain folders from solution (and build) except one in .NET5?

Question

Consider the following file structure:

• /Themes
  • /Default
  • /Theme-1
  • /Theme-2
  • /Theme-3

Is it possible to exclude all folders except the 'Default' folder?

MSDocs seem to suggest this is, or was, possible.

<Compile Include="*.res" Exclude="Form1.cs">

However, when I apply the following structure per the documentation, visual studio throws the following errors:

xxx.csproj : error  : At most one of the include, remove, and update attributes may be specified for an item element.

When I simply add one exclude for all files followed by a separate include for the file I want to retain, it simply hides all files. Does anyone have any idea how to exclude all folders except certain ones?