JNLP has been deprecated in java. OpenWebStart is a re-implementation for newer Java Versions: https://openwebstart.com/
I installed this application, downloaded the .jnlp file from my ISY, and was able to run with OpenJDK 11 (looks like it was installed as part something on the MS side). I'm going to try to upgrade to OpenJDK 18, but OpenWebStart worked great.