Ensure that IsDarkModeEnabled always returns a valid result.

Author: KlausLoeffelmann

src/System.Windows.Forms/src/System/Windows/Forms/Application.cs

@@ -328,7 +328,9 @@ public static DarkMode EnvironmentDarkMode
             {
                 DarkMode.Enabled => true,
                 DarkMode.Disabled => false,
-                _ => throw new InvalidOperationException("DefaultDarkMode is not set.")
+
+                // We return false even if DarkMode is not supported so that we ALWAYS have a valid result here.
+                _ => false
             }
         };
 

src/System.Windows.Forms/src/System/Windows/Forms/Controls/PropertyGrid/PropertyGrid.cs

@@ -1621,7 +1621,9 @@ private PropertyGridView CreateGridView(IServiceProvider? serviceProvider)
     }
 
     [Conditional("DEBUG")]
+#pragma warning disable CA1822 // Mark members as static
     internal void CheckInCreate()
+#pragma warning restore CA1822 // Mark members as static
     {
 #if DEBUG
         if (_inGridViewCreate)

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/StatusStripTests.cs

@@ -121,8 +121,11 @@ public void StatusStrip_Ctor_Default()
         Assert.Null(control.Region);
         Assert.NotNull(control.Renderer);
         Assert.Same(control.Renderer, control.Renderer);
-        Assert.IsType<ToolStripSystemRenderer>(control.Renderer);
-        Assert.Equal(ToolStripRenderMode.System, control.RenderMode);
+
+        // TODO: Assume control.Renderer can be either ToolStripSystemRenderer or ToolStripProfessionalRenderer for the Moment.
+        Assert.True(control.Renderer is ToolStripSystemRenderer or ToolStripProfessionalRenderer, "Renderer is not one of the expected types.");
+        Assert.True(control.RenderMode is ToolStripRenderMode.System or ToolStripRenderMode.ManagerRenderMode);
+
         Assert.True(control.ResizeRedraw);
         Assert.Equal(200, control.Right);
         Assert.Equal(RightToLeft.No, control.RightToLeft);
@@ -1257,15 +1260,15 @@ private class NonReadOnlyControlsStatusStrip : StatusStrip
 
     private class SubStatusStrip : StatusStrip
     {
-        public new const int ScrollStateAutoScrolling = StatusStrip.ScrollStateAutoScrolling;
+        public new const int ScrollStateAutoScrolling = ScrollableControl.ScrollStateAutoScrolling;
 
-        public new const int ScrollStateHScrollVisible = StatusStrip.ScrollStateHScrollVisible;
+        public new const int ScrollStateHScrollVisible = ScrollableControl.ScrollStateHScrollVisible;
 
-        public new const int ScrollStateVScrollVisible = StatusStrip.ScrollStateVScrollVisible;
+        public new const int ScrollStateVScrollVisible = ScrollableControl.ScrollStateVScrollVisible;
 
-        public new const int ScrollStateUserHasScrolled = StatusStrip.ScrollStateUserHasScrolled;
+        public new const int ScrollStateUserHasScrolled = ScrollableControl.ScrollStateUserHasScrolled;
 
-        public new const int ScrollStateFullDrag = StatusStrip.ScrollStateFullDrag;
+        public new const int ScrollStateFullDrag = ScrollableControl.ScrollStateFullDrag;
 
         public new bool CanEnableIme => base.CanEnableIme;