WandaVision would be an easier sell if the second half of the season was as interesting as the first half. I really dug all the sitcom stuff and the undercurrent of horror rippling through there, but it kind petered out for me once it turned into the usual Marvel fare in the back half of the season.
Going into Multiverse of Madness simply knowing that in her post-Infinity War/Endgame grief, Wanda used her magic to manifest children and hold a town hostage to her whims while she and her 'artificial' family lived there as though nothing was wrong – and that now she has lost that family as well – should suffice.