I’m surprised that you are unable to run the demo since it only uses text. I’m a Mac user but do have a Windows 11 system so I will see if I can get something that you can run. In the meantime here are a couple of references so that you can see what has been done in the past. To make a long story short the only way that I know of to use all the javafx modules with Processing 4 is to modify the Processing source code to add the ones that were left out by the authors. A request was made to the authors to add them, but to date this has not been done. However, you could do it yourself by editing the source code (Processing IDE is open source) and re-compiling the editor. I’ve done it but it is somewhat cumbersome and is not easy. You also might try an older version of Processing, eg version 3.x.x since it included more of the modules.
References: https://discourse.processing.org/t/javafx-unable-to-add-modules-to-processing-ide/41272
https://github.com/processing/processing4/issues/522
Addendum:
Make sure that there is a ‘javafx’ folder inside of your ‘libraries’ folder in your sketchbook. You can go to the Preferences menuItem in the Processing app to see where that is located on your system. You also need to make sure that it is installed to start with: use Tools/ManageTools/Libraries/JavaFx to see if has a check mark beside it. On Windows it could be installed but just not where it needs to be. You should be able to run the simple demo that I posted if the file is where its expected to be.
Addendum2: For whatever it’s worth, I have the ‘javafx’ folder inside my ‘libraries’ folder in my Processing folder in Windows 11 and it still won’t run. Don’t know why.