I have recently tried to follow this article here: https://www.esri.com/arcgis-blog/products/story-maps/mapping/embedding-a-story-map-within-a-story-map/ I was trying embed this map story https://arcg.is/1uqiPK within this one https://arcg.is/0TT9ie (HES tab) this is to avoid a double title as. However, the moment I add to the link the “&embed” the link will stop working! I found out you have to use the long URL that can be extracted from the "Embed" sharing option only! this is not mentioned in this article! So, though that will help others.
Also, you may be interested about this issue (related to embeding Tabealu into Map Story) which I have sorted recently: https://community.tableau.com/message/915304#915304