The installed application would not launch on linux. The application log showed that the 
jpackage application launcher couldn't find a jvm lib. Graal appears to handle this 
differently for libjli.so by putting it into it's own directory.

So the workaround was to 'cd' into the graal directory
graalvm-ce-java11-21.1.0/lib/runtime/lib
and then
ln -s jli/libjli.so

Putting a libjli.so where jpackage expects it. 
I wasn't sure this would work with the .deb file but it appears to.