Thanks for the comments. Those example buildings will help!

Regarding java on the Mac (Monterrey), I am getting ok results invoking via Terminal and using

java -jar OSM2World.jar

or

java -jar –add-modules ALL-SYSTEM josm-tested.jar

Java version:

java –version openjdk 11.0.8 2020-07-14 LTS OpenJDK Runtime Environment Zulu11.41+23-CA (build 11.0.8+10-LTS) OpenJDK 64-Bit Server VM Zulu11.41+23-CA (build 11.0.8+10-LTS, mixed mode)