The Darkhold made an appearance before Doctor Strange 2 and WandaVision

gamesradar.com:

Doctor Strange in the Multiverse of Madness may have introduced plenty of new characters and concepts, but one of its most important can trace its origins back to before Doctor Strange 2, before WandaVision – and into a Marvel project that now has murky ties to canon.

Even so, it’s a lineage that is incredibly important given the mystic nature of the sequel, Scarlet Witch’s involvement, and its links to a Doctor Strange villain. Read on as we discuss the unlikely starting point for one of the MCU’s most powerful objects.

Spoilers for Doctor Strange in the Multiverse of Madness follow. You have been warned.

Yes, the Darkhold is brought back in Doctor Strange 2. Last seen during the WandaVision finale, the tome – or Book of the Damned, as Agatha called it – features a catalog of dark and forbidden spells. During Multiverse of Madness, for instance, Wanda uses it to ‘Dreamwalk’, which sees jer temporarily taking over another version of herself in the multiverse.

We discover that the physical book of the Darkhold is a copy of the spells etched into the walls in Chthon's tower on Mount Wundagore. That’s a similar origin to its comic book counterpart. There, it’s formed from the writings of an Elder God named Chthon, also known as the Archdemon of Chaos. Its genesis in the Marvel shows and movies, however, can be found in Agents of SHIELD.

In the series, the book is uncovered by Lucy and Joseph Bauer during the fourth season. It caused so much chaos and destruction that it was eventually taken into Hell by Ghost Rider. It later appeared in another Marvel series, Runaways, and was obtained by Morgan le Fay – who ultimately ended up banished from Earth.

From there, it ended up in the hands of Agatha Harkness, before being