Simple Answer: jDeploy. Steve Hannah wrote this beautiful Software which generates installers for all System platforms and builds them up for Download on Github or npm. If you have an already ready .jar file or you start a new Java project: with Deploy you can do the entire Job with a Desktop GUI. And the best of it: it is for free and costs: zero Bucks.
With Deploy you can deploy from all platforms to all platforms, no need to run build tasks for these platforms. Notarization for macOS is also included. No crappy work with apple, just jDeploy and the job is done.
You’ll find jDeploy here: https://jdeploy.com