What about people the use Oracle JDK and don't want to be forced to install OpenJDK + OpenJFX?

Feel free to contribute a fix, but don't force people to use a specific runtime or dependencies that may or may not be available for their platform via the official repository.
not forcing anything on ...

your debian package needs to have openjfx as a requirement. it currently does not and so the application (although it loads) fails to be able to do anything meaningful.