You can pack .jar in .app (inside dmg that has drag and drop) with Javapackager like this:
javapackager -deploy \ -title "YourTitle" \ -name "Name" \ -appclass your.class.start \ -native dmg \ -outdir ~/Downloads \ -outfile yourOutFileWithoutExtension \ -srcdir "SourceDir"
you can use -srcfiles Your.jar if its only one jar.
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