Program.cs

// Replace this line:
// using System.Windows.Forms;
// With:
using System.Windows.Forms; // Ensure your project targets .NET Framework or references System.Windows.Forms.dll

// If you are targeting .NET Core or .NET 5+, add a reference to the NuGet package 'System.Windows.Forms'.
// In Visual Studio, right-click your project > Manage NuGet Packages > Browse > search for 'System.Windows.Forms' and install it.

// If you are using a .NET Core/5+/6+ project, also ensure your project file (.csproj) includes:
//
// <ItemGroup>
//   <PackageReference Include="System.Windows.Forms" Version="*" />
// </ItemGroup>
//
// And set the project property:
// <UseWindowsForms>true</UseWindowsForms>
//
// Example:
// <PropertyGroup>
//   <OutputType>WinExe</OutputType>
//   <TargetFramework>net6.0-windows</TargetFramework>
//   <UseWindowsForms>true</UseWindowsForms>
// </PropertyGroup>