The runShadow task is using the output of the shadowJar task as the argument to java -jar .... This resolves to a path in build/libs but that is not where the shadow configuration jars are copied to. Thus, any dependent libraries (like encryption libraries) are not available.

Instead, runShadow should depend on installShadowApp since that task will write the -all jar and the dependent jars from the shadow configuration to the build/installShadow/<project-name>/lib directory and the argument path should be in the location in that directory. That way, dependent jars that are included in the manifest Class-Path attribute will be in their correct relative locations.