AutoCursor.cs

// Create a class like this

public class AutoCursor : IDisposable
{
    private Form form;

    public AutoCursor (Form form)
    {
        this.form = form;
        
        form.Cursor = System.Windows.Forms.Cursors.WaitCursor;
    }

    public void Dispose ()
    {
        if (form.Cursor == System.Windows.Forms.Cursors.WaitCursor)
            form.Cursor = System.Windows.Forms.Cursors.Arrow;
    }
}


// Then use it like this
using (new AutoCursor (this)) {
  // Long running process here...
}

This is so simple, yet great! I should have thought of this long ago. I didn't but I'm glad you did.