I created a folder structure with an folder with an JavaFX project in it. If I open only this folder who contains JavaFX within IntelliJ everything gets imported correctly and the sample main is running. If I open the whole project where the folder with JavaFX is an subfolder only I get a lot of red and running the main results in many errors. How can I open a JavaFX project within another project in IntelliJ?
IntelliJ Project structure if it does work
GUI +-- JavaFXRelatedFiles
IntelliJ Project structure if it does not work
+-- src | +-- GUI | +-- OtherFolder
File | New Module... instead of
File | New Project....
The setup of the new module after that will be similar to the new project, so you can just follow the instructions you linked for creating a new JavaFX project.
If you want to link the multiple modules together with a Maven build, that is much more complex (especially if you use both maven and java platform modules), so I won’t describe that process here.