Hello @Helmut243151150cd5,
I'm sorry to hear that you're experiencing issues with the Illustrator 28.0 Beta not starting. We've just released Ai beta v28.0.30 today. You can update this by opening the Creative Cloud Desktop App, going to the Apps > "Updates" section, and clicking the "Check for Updates" button.

If this doesn't help, could you please share the logs via DM using the steps in this article (https://helpx.adobe.com/creative-cloud/kb/cc-log-collector.html)? These logs can provide valuable insights into what might be causing the error and help us diagnose the problem more effectively.
Also, please confirm if you're running the regional locale version of Illustrator or the generic global English version.
With this information, we'll have a better understanding of the issue and be able to provide more specific guidance to help you resolve it. Feel free to share any other details that might be relevant as well.
Looking forward to assisting you further!
Best regards,
Anshul Saini