They’ve introduced Control center for organizations, I’m not sure if that will have any effect. But in case the basic roles were modified at the org level then it could have happened that the permissions are not sufficient – This is only a guess. Maybe someone has better suggestions on this.
You could reach out to Mendix support team if nothing works and there are no suggestions.
I checked and I still have the button:
So if you see something different create a support ticket on support.mendix.com