Platforms namespace gone

Thanks, but none of these were relevant.

I finally solved the issue by changing the Windows target framework to windows10.0.20348.0:

<TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('windows'))">$(TargetFrameworks);net9.0-windows10.0.20348.0</TargetFrameworks>

from

<TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('windows'))">$(TargetFrameworks);net9.0-windows10.0.19041.0</TargetFrameworks>