There is another thread open with a similar/same issue, but I need to push this topic and the creator of the other thread is not responding.
We have the issue that we cannot chose a Notification scheme. The page is broken.
Reason:
We switched in the Project Settings -> Notifications -> The notification scheme to "None".

And after you switch it, you dont have the option to switch back to another. The whole right frame stays blank:

And if you try to solve it from the other direction: You can create a new "Notification scheme", but there is no option to assign this to a Project.
This issue is reproducible.
How can I fix it?