The limited amount of information released about The Death of Doctor Strange #4 teases that the identity of the new Sorcerer Supreme will be revealed. This is part of the five-issue limited series that serves as the epicenter for Marvel's The Death of Doctor Strange event. It has been exploring the impact on the Marvel Universe as a whole as it's threatened by supernatural forces after the mysterious murder of Doctor Strange.
The Death of Doctor Strange is written by Jed MacKay (Black Cat) with artwork by Lee Garbett (Loki: Agent of Asgard). In the third issue, a threat on par with the Black Order appears in the form of "The Three Mothers": the Wyrd, the Crown, and the Crawling. There will also be numerous tie-in one-shots playing a role in the event, including The Death of Doctor Strange: White Fox #1, which features White Fox trying to clear her name after being framed for Doctor Strange's murder. Other heroes involved in the event include Ben Reilly and Black Cat in a Spider-Man tie-in as well as Strange Academy.
Marvel Comics teased the fact that the next Sorcerer Supreme will be identified in The Death of Doctor Strange #4 when it announced plot details for the fourth issue. Along with showcasing the cover for the fourth issue by Kaare Andrews (Iron Fist: The Living Weapon, Amazing Fantasy), the press release clearly lays out that "a hero steps up to resume the duties of the Sorcerer Supreme." So the answer of who will be filling this hole in the Marvel Universe will be answered in December.
There have been plenty of powerful versions of the Sorcerer Supreme in comics, ranging from Iron Man to Loki. Some of these sorcerers hail from alternate universes, while others are part of the Earth-616 continuity. It will be interesting to see if the comic event will pull a previous character who has held the mantle, introduce a completely new character, or most likely, announce an established character who will become the next Sorcerer Supreme.
In this same announcement, two other tie-in books were announced. There is Death of Doctor Strange: Blade, which explores the role of vampires in the story, written by Danny Lore with artwork by Dylan Burnett. The other one will be Death of Doctor Strange: X-Men/Black Knight by the Way of X creative team Si Spurrier and Bob Quinn. That story will feature a fight between the mysteriously transformed X-Men against Ebony Blade bearers Dane Whitman and his daughter Jacks, along with Excalibur's wielder Faiza Hussain. These particular one-shots will be released in December 2021, the same month that The Death of Doctor Strange #4 will reveal the identity of the new Sorcerer Supreme of the Marvel Universe.
Source: Marvel Comics