net6.0-windows 
namespace System
{
    public sealed class OperatingSystem : ICloneable, ISerializable
    {
        public static bool IsFreeBSDVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);
    }
}
nuget.org
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Reference this API
.NET
5.06.07.08.09.010.0
Information specific to net6.0
Assembly

System.Runtime , Version=6.0.0.0, PublicKeyToken=b03f5f7f11d50a3a

Referencing

Your project needs a package reference to System.Runtime.Experimental.

Package System.Runtime.Experimental (6.0.2) net6.0
Platform Restrictions

This API is supported on all platforms.

  • Built-in API
  • Package-provided API