jSerial and B4J Packager 11
jSerial depends on a native library named jssc.dll. It is included inside jssc.jar, under the natives folder. Remember that a jar file is actually a zip file.
This dll should be copied to build\bin folder, after you ran B4JPackager.
For your convenience the dll for Windows 64 bit is attached. Note that Windows 32 bit is not supported by Java 11+.