After pressing some keys like ↖ (KeyEvent.VK_HOME), ↘ (KeyEvent.VK_END), ⌦ (KeyEvent.VK_DELETE) and releasing them by java.awt.Robot the [fn] looks like pressed but not released.
Here is an example

import java.awt.*;
import java.awt.event.KeyEvent;

public class MacFnReproducer {

    public static void main(String[] args) throws AWTException {
        final Robot robot = new Robot();
        robot.keyPress(KeyEvent.VK_END);
        robot.keyRelease(KeyEvent.VK_END);

//robot.keyRelease(KeyEvent.VK_RIGHT);

        robot.delay(2500);
        robot.keyPress(KeyEvent.VK_C);
        robot.keyRelease(KeyEvent.VK_C);
        robot.delay(2500);
    }
}

During execution of this app on macOS Monterey (e.g. 12.3.1) the Notification Center window appears (on the upper right corner) like the combination [fn]+[c] was pressed. The issue was not observed on BigSur (probably because the shortcut [fn]+[c] does not work there).

Please note if after releasing KeyEvent.VK_END to invoke releasing KeyEvent.VK_RIGHT then [fn] is also released and press-release [c] works as expected i.e. Notification Center does not appear.

The issue was observed with

openjdk version "19-ea" 2022-09-20
OpenJDK Runtime Environment (build 19-ea+20-1369)
OpenJDK 64-Bit Server VM (build 19-ea+20-1369, mixed mode, sharing)

It can be reproduced with 11, 17 as well.
It cannot be reproduced with 8