How to provide Platform implementations for net9.0 target framework with SingleProject

[Dreamescaper]

So I have a type, which is implemented differently per platform via Platform folders:
Platforms/Android/MyType.cs
Platforms/iOS/MyType.cs

It works fine, but now I want to add tests for this project. Therefore, I'm adding net9.0 target framework (platformless), and I need to add MyType.cs (fake implementation) for this target framework.

Is there any way to add "platformless" Platform folder?

I have tried to add this to my csproj:

 <MauiPlatformSpecificFolder Include="Platforms\Standard\" TargetPlatformIdentifier="" />

And add it to Standard folder. It doesn't work, however.

Is there any better way to do that?