ubuntu – JavaFX 2nd window gets hidden in the taskbar

I’m a student and i have a project where to create a desktop app using java.
I have started a tutorial and apparently I got stuck with few issues.

I managed to create a window with a button that gets me to a second window however the second one goes in the task bar.enter image description here

Another issue I face and it’s hard to understand what is the right module path to add into IntelliJ. The tutorial has a specific one where I can’t get to find it. Due to the lack of experience I have downloaded one from JavaFX website to match the requirements but errors occur.
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I also would like to upload the tutorial example with that specific path:

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Where mine looks like:

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I doubt that the code is wrong. It seems to be more like version match of the path.
Please help me
Thank you