Latest official version of JDemetra+, released on October 21st 2024, can be found at
https://github.com/jdemetra/jdplus-main/releases/tag/v3.3.0
For installing instructions see https://jdemetra-new-documentation.netlify.app/#installing-the-software
Note that Java 21 is now embedded is in the installation files, you don’t need to tackle this issue on your computer. Be sure to choose the windows specific zip file (if you use windows).