Avalonia/src/Avalonia.Base/Platform/IRuntimePlatform.cs

using System;
using Avalonia.Metadata;

namespace Avalonia.Platform
{
    [PrivateApi]
    public interface IRuntimePlatform
    {
        RuntimePlatformInfo GetRuntimeInfo();
    }

    [PrivateApi]
    public record struct RuntimePlatformInfo
    {
        public FormFactorType FormFactor => IsDesktop ? FormFactorType.Desktop :
            IsMobile ? FormFactorType.Mobile : FormFactorType.Unknown;
        public bool IsDesktop { get; set; }
        public bool IsMobile { get; set; }
    }

    public enum FormFactorType
    {
        Unknown,
        Desktop,
        Mobile
    }
}