Where Is The Mind Flayer During Stranger Things 4 Volume 1?

One of the most chilling powers Vecna displays is his ability to reach out to our dimension after attaching himself to a set of creepy tendrils in the Upside Down. As the show makes clear, though, these aren't a part of his actual body. You see him walking around in possessed people's minds without any extra appendages, and the tentacle-things clearly attach to him from an unseen source in the Upside Down. What's more, the revelation of Vecna's true identity confirms that his base appearance is very much that of a human, and exposure to the elements of the Upside Down have molded him into what he is today. Still, those fleshy tendrils remain unexplained ... that is, unless he's managed to tap into the powers of some hitherto unseen Upside Down force.

Which brings the discussion to the Mind Flayer. The creature is all about mind control and creepy tendrils, and it's been heavily implied to preside over the Upside Down with its powers. Could the tentacles Vecna is using to boost his powers belong to the Mind Flayer? Has the Mind Flayer voluntarily joined forces with Vecna to rain terrible vengeance upon the people of Hawkins, who have foiled its plans so many times? Or has Vecna challenged the Mind Flayer over the control of the dark alternate dimension, and gained control of its powers?