According to the spec:

--mac-bundle-name <name string>
      Name of the application as it appears in the Menu Bar. This can be different from the application name.

1. set --mac-bundle-name to "TestBundleName"
jpackage create-installer --installer-type pkg --input input --output output --name hello-1.0.pkg --main-jar hello.jar --main-class Hello --mac-bundle-name TestBundleName

2. Install hello-1.0.pkg and run the app.

3. See the app name in the system menu
obtained: hello
expected: TestBundleName