EtoApplication.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <RootNamespace>EtoApplication</RootNamespace>
    <PackageVersion>1.0</PackageVersion>
    <Title>EtoApplication</Title>
    <Copyright>Copyright © 2018</Copyright>
    <Description>Description of EtoApplication</Description>
    <OutputType>Exe</OutputType>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Eto.Forms" Version="2.4.1" />
    <PackageReference Include="Eto.Platform.Gtk" Version="2.4.1" />
  </ItemGroup>
</Project>

EtoApplication.sln

Microsoft Visual Studio Solution File, Format Version 12.00
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EtoApplication", "EtoApplication.csproj", "{A0FD19D5-9A64-4457-98D3-20AB569C2488}"
EndProject
Global
	GlobalSection(SolutionConfigurationPlatforms) = preSolution
		Debug|Any CPU = Debug|Any CPU
		Release|Any CPU = Release|Any CPU
	EndGlobalSection
	GlobalSection(ProjectConfigurationPlatforms) = postSolution
		{A0FD19D5-9A64-4457-98D3-20AB569C2488}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
		{A0FD19D5-9A64-4457-98D3-20AB569C2488}.Debug|Any CPU.Build.0 = Debug|Any CPU
		{A0FD19D5-9A64-4457-98D3-20AB569C2488}.Release|Any CPU.ActiveCfg = Release|Any CPU
		{A0FD19D5-9A64-4457-98D3-20AB569C2488}.Release|Any CPU.Build.0 = Release|Any CPU
	EndGlobalSection
EndGlobal

MainForm.cs

using System;
using Eto.Forms;

namespace EtoApplication
{
    public class MainForm : Form
    {
        public MainForm()
        {
            Title = "My Eto Form";
            Content = "Hello World";
            Menu = new MenuBar
            {
                Items =
                {
                    new ButtonMenuItem
                    {
                        Text = "Disabled",
                        Enabled = false,
                        Items =
                        {
                            new ButtonMenuItem
                            {
                                Text = "Cannot see this"
                            }
                        }
                    },
                    new ButtonMenuItem
                    {
                        Text = "Disabled but clickable",
                        Enabled = false,
                        Command = new Command((s, a) => MessageBox.Show("Disabled but clickable clicked"))
                    }
                }
            };
        }
        
        [STAThread]
        static void Main(string[] args)
        {
            new Application(Eto.Platform.Detect).Run(new MainForm());
        }
    }
}