Window decorations:

- enabled `TitlePane.unifiedBackground` by default (because seems to be standard on Windows 11)
- no longer paint a bottom separator for the menu bar (if unified background is enabled)

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatMenuBarBorder.java

@@ -53,6 +53,9 @@ public class FlatMenuBarBorder
 
 	@Override
 	public void paintBorder( Component c, Graphics g, int x, int y, int width, int height ) {
+		if( !showBottomSeparator() )
+			return;
+
 		float lineHeight = scale( (float) 1 );
 		FlatUIUtils.paintFilledRectangle( g, borderColor, x, y + height - lineHeight, width, lineHeight );
 	}
@@ -68,4 +71,9 @@ public class FlatMenuBarBorder
 		insets.right = scale( margin.right );
 		return insets;
 	}
+
+	/** @since 2 */
+	protected boolean showBottomSeparator() {
+		return !UIManager.getBoolean( "TitlePane.unifiedBackground" );
+	}
 }

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLaf.properties

@@ -709,7 +709,7 @@ TitledBorder.border = 1,1,1,1,$Separator.foreground
 
 TitlePane.useWindowDecorations = true
 TitlePane.menuBarEmbedded = true
-TitlePane.unifiedBackground = false
+TitlePane.unifiedBackground = true
 TitlePane.showIcon = true
 TitlePane.noIconLeftGap = 8
 TitlePane.iconSize = 16,16