Solution found and implemented. See below original post.
My JVM installation apparently does not contain javaws.
$ sudo update-alternatives --get-selections | grep ^java java manual /usr/lib/jvm/java-12-oracle/bin/java javac manual /usr/lib/jvm/java-12-oracle/bin/javac javadoc manual /usr/lib/jvm/java-12-oracle/bin/javadoc javap manual /usr/lib/jvm/java-12-oracle/bin/javap
javaws to launch a
jnlp file. The app apparently needs the Oracle distribution and not OpenJDK.
I tried v11 and v8 but PPA appears to be unavailable due to new licensing.
This is not a duplicate of not able to install javaws because webupd8team's PPA and oracle-java8-installer doesn't exist anymore due to new licensing:
javaws does not appear to be in the main v12 distribution as per the directory structure.
SOLUTION: Do not use ppa, Register for Oracle Network, download JDK8, install manually. javaws does not exist for v11+
Install JVM manually using: https://linuxconfig.org/how-to-install-java-on-ubuntu-18-04-bionic-beaver-linux