We rely on a proper OSGi classpath. So we can avoid ClassLoading problems and dependency resolution conflicts (aka JAR-Hell).
Trying to run normal Java-Code with our OSGi bundle JARs is not recommended or supported. So you should not use your own Main class or similar. But you can run any java code safely within our IvyProject environment.
If you face classloading issues in build process with maven you could share a flat classpath of the engine to provide build dependencies. But not to run an Java process on it. See https://axonivy.github.io/project-build-plugin/release/7.0/share-engine-core-classpath-mojo.html