Hi Andreas Zeitler,
Welcome to Microsoft Community.
Unfortunately, this is the same problem we are facing.
One possibility is that unstable network factors are preventing Workspace-related code from completing the initialization process.
Based on the information in the Workspace-related articles, there are some prerequisites for using Workspace.
Microsoft Edge Workspaces | Microsoft Learn
Besides, for similar cases, many community members recommend observing whether the situation is the same with a new Profile state.
If the situation remains the same, it's more suitable to submit the information to the product team for further investigation and analysis.
- Microsoft edge Workspace error, unable to load. - Microsoft Q&A
- Microsoft Edge Workspaces | Microsoft Learn
- Edge Workspace Error: Unable to Load - Microsoft Q&A
You may submit feedback in the Microsoft Edge browser as well. Open the page in the Microsoft Edge browser, then use the shortcut keys "Alt" + "Shift" + "I" to open the feedback window or select the 3 dots in the top right, select Help and feedback, then choose Send feedback (Note that the feedback window will capture the current screen and URL link and email address, and you can add Attachment and record your problem), enter your problem, and click "Send".
If I misunderstand your situation, feel free to correct me and share the information.
Thanks for your patience and cooperation.
Best Regards,
Kyo - MSFT | Microsoft Community Technical Support