In Java 11 the JavaFX components have been removed into their own SDK, so when you run it won't be able to find them in the runtime.
The JavaFX page has the instructions to get it going: https://openjfx.io/openjfx-docs/#install-javafx
In short, you have to compile / run by adding the javafx modules in, either as options passed on the command line, or using a modular project.
I found that the modular project with Maven and IntelliJ worked best for me. https://openjfx.io/openjfx-docs/#IDE-Intellij
In the modular method you have a module-info.java
file that describes all the modules that your project "requires", and allows you to "open" them to other modules. If you have a bunch of Maven dependencies you have to add them in the requires list too though. (IntelliJ can make this easy - find the error about no requires in the code and alt-enter)
Once everything was working with modules etc, I had to make a Fat Jar using I think the Maven shade plugin, to put everything together. Then it would work running the jar from the command line.
However, after getting my Java 11 code @#$%@# working after 2 days of pain, I went back to Java 8 (using correto SDK for latest version) as Java 11 doesn't have packaging and IntelliJ can't do it for you.