The book was used by them to imprison Morgan in her Dark Dimension.
The book was also used in the final season of Marvel’s Runaways by Morgan le Fay in an attempt to bring the Dark Dimension to the Earth Plane but she was stopped by the Runaways and PRIDE.
The Darkhold was fundamental to the third part of Agents of S.H.I.E.L.D. Season 4 as it was used to create the virtual world known as the Framework, which was used to trap several S.H.I.E.L.D. agents in a simulated reality.
It was also used by Aida to create herself a human body using the dark matter, but the Darkhold would soon be taken to Hell by S.H.I.E.L.D. and Ghost Rider.