creating a runnable JAR file _ missing VM arguments _ only runs with the IDE

I've made a JavaFX application using eclipse, but sadly it does only work while running with the IDE.

When exporting the project as a runnable jar file, eclipse notes:

I guess it has something to do with JAR file missing the VM arguments. I don't know how to add them though.

When running through the terminal I get this:

I would the very thankful if you could help me get it running. I've heard something about putting the file into a package, I am a bloody beginner though, and need a little help here.

I don't think it matters much, but I am using MacOS.

I need it as an executable file, so I just have to double click on the file and it runs. I need it for both MacOS and Windows.

If any further details are needed I will provide them.

Thanks in advance.