jWebSocketClient v2.00 is attached. It requires Java 11+.
It solves the wss connection issue. It wasn't fully tested so consider it a beta version.
The instructions are a bit more complicated than usual:
1. jWebSocketClient.xml + jar go into the internal libraries folder.
2. The other two jars from the second zip go into internal libraries folder\jserver
Add this in order to build a standalone package:
#AdditionalJar: jserver/jetty-webapp-11.0.9.jar
#PackagerProperty: AdditionalModuleInfoString = provides org.slf4j.spi.SLF4JServiceProvider with org.eclipse.jetty.logging.JettyLoggingServiceProvider;
#PackagerProperty: IncludedModules = jdk.charsets, jdk.crypto.ec