Hi, for using this toolchain with Java I would recommend the use of Java 17, the current LTS Version of the Java JDK. So you should download and install the OpenJDK, I recommend here AZUL OpenJDK which you’ll find here: Java Download | Java 7, Java 8, Java 11, Java 13, Java 15, Java 17, Java 19 - Linux, Windows & macOS and I recommend to choose the installer for your OS (MacOS DMG, Debian DEB, Windows MSI.
After you have installed the Java OpenJDK 17 you are ready to go for installing IntelliJIdea Community Edition which you find here: Download IntelliJ IDEA: The Capable & Ergonomic Java IDE by JetBrains and install it. You will find Versions for MAC X86 and M1 and also for Windows and Linux.
Now starting IntelliJ first time you go to preferences, plugins, marketplace and install the JFormdesigner Plugin.
That’s it. Now you can write all Applications for Desktop you want, including graphics, Office automation and so on. Nothing else needed. Even for working with Vaadin and CodenameOne for Web and mobile Development you do not need to install anything else, they have Starter Projects which install all needed Dependencies.
That would be in my eyes a good and fast replacement for Xojo for only 50$ per year. If you want to compile IOS and Android Apps not by self but with the Build Servers you can even get their Software as a Service including Buildservers for small projects for free.