I do not know if this Theory makes Sense to people and if its new or an old Theory, I been watching Voyager First Contact in wake of the Star Trek Picard Trailer and the Theories that Dahj is actually a Former Borg Queen. I am here to tell you She is not and here is why i think that is! We See the Borg as a Hive mind one mind in control over everything, and to organize these thoughts the collective created a Hub that can organize the Thought Patterns of Trillions of Drones that's where the Queen Sets in. She was not to Control the Hive but to kept minds Organize and P refection but there was a Glitch in the Programming of the Hub and thus the Queen is Born she as the mind of her own and thus begun to control the collective. The Queen in herself is basically a Glitch and with this craziness of perfection in controlling all life in the universe She basically the Reason why the Borg sought Perfection because Queen her self is a glitch and she need to satisfy her self for Perfection. So where dose Dahj fit in to all this why the Theory of her not the Queen well the Queen is Program that lives in the Hive and she uses Borg Avatars that she Creates to interact with Beings that she find most fascinating as well able to interact with the Collective personally but this is a Failed in it self we seen in Endgame and in First Contact when the Queen Dies so dose the collective and why is that because She is a Hub and she should be living with in the Collective herself. Unless she makes Back up of her self with in the Subspace network of the Borg Collective the Borg Will Die that is why Dahj is not the Queen and why the Queen is a major Glitch and Weakness with in the collective!!!
May the Shwartz Be With You