The jpackage tool has now the option to provide a tiff with high resolution for Mac OS retina
displays. JabRef should also provide a high resolution image.

Refs: https://bugs.openjdk.java.net/browse/JDK-8234284

Some tutorials. It seems to be someone with a mac is required.

https://computers.tutsplus.com/tutorials/how-to-create-a-retina-ready-dmg-based-app-installer--cms-21653

https://developer.apple.com/library/archive/documentation/GraphicsAnimation/Conceptual/HighResolutionOSX/Optimizing/Optimizing.html