Considering I never saw Wandavision myself? No. Hard to understand something you never saw.
Okay, well, that scene gives a reason for her behavior in the movie. The Darkhold is a corrupting influence*, and she fully immersed herself in it for some time, embracing its power trying to get back what she has lost.
They also mentioned that now Doctor Strange has the Darkhold. Does that mean he is going to murder-monster people? Is that the impact of the Final Scene of Multiverse of Madness?
I expect he'll see some impact of using it, but he was more aware of what he was dealing with, used it to a limited degree, and hasn't been as traumatized as Wanda, so... who knows where they'll take it.
*In the comics continuity, it is, for example, the book containing the spell that created the first vampire.