Juergen Mayrbaeurl I'm glad that your issue is resolved and thank you for posting your solution so that others experiencing the same thing can easily reference this!
Since the Microsoft Q&A community has a policy that the question author cannot accept their own answer, they can only accept answers by others, I'll repost your solution in case you'd like to Accept the answer.
Error Message:
By default the OPC PLC simulator doesn't get installed on deploying Azure IoT Operations to the Kubernetes cluster. Is there a way to install it manually afterwards?
Solution:
After doing a helm upgrade for opc-ua-broker with --set opcPlcSimulation.deploy=true it now works for me
If you have any other questions, please let me know. Thank you again for your time and patience throughout this issue.