Update: Unfortunately, we no longer allow embedding of dashboards on Grafana Cloud at all. That feature requires access for anonymous users to your instance to work properly which we don’t allow in Grafana Cloud for security reasons. You can read more about the security implications of the anonymous feature here.
We now have a feature called public dashboard that may be of interest. It has some limitations which are described in the link. If you’d like this feature enabled, please reach out to Support.