The behavior of the decorated full-screen window is not specified:
https://docs.oracle.com/en/java/javase/11/docs/api/java.desktop/java/awt/GraphicsDevice.html#setFullScreenWindow(java.awt.Window)

But it will be good to have the same cross-platform behavior. This bug is about Linux.
Modify the test: open/test/jdk/java/awt/FullScreen/FullscreenWindowProps/FullscreenWindowProps.java

Remove frame.setUndecorated() and tweak the size variation in the checkSize().
The problem is that the bounds of the frame include insets additionally to the screen size.

see JDK-8256201