Maven project is still available.
When I open it in Netbeans 11 it always think of it as a Gradle Project. I deleted anything that says gradle and Netbeans almost understood it was a Maven project. Now it's broken.
Personally I would recommend to use IntelliJ IDEA. Much better IDE and works fine with gradle. That's what we use for development.
It worked on Eclipse. Just imported existing Maven project into workspace and run Main using debug.xml as argument. Just like I used to do with Netbeans.
By the way, Eclipse is not bad with Maven anymore. You guys could update this: https://www.traccar.org/build/
Up to 4.6 I always followed these instructions: https://www.traccar.org/build-in-netbeans/
Now I pulled 4.8 from github and it looks like there was a change from Maven to Gradle. With Gradle there are lots of tasks but none to run the project.