One of the best episodes in Marvel's What If...? series, at least in my opinion, was Episode 5, "What If... Zombies?!" The episode took us to a universe in which The Avengers are infected by a zombie plague and the remaining surviving heroes must search for a a cure.
With the episode receiving praise from many, it seems Marvel is keen on expanding upon this concept. Announced during Disney Day+ 2021 was Marvel Zombies, a new animated series that "reimagines the Marvel Universe as a new generation of heroes battle against an ever-spreading zombie scourge."
The series will be directed by executive producer Bryan Andrews and written by executive producer Zeb Wells. That's about as far as the description or details for the new animated series went so the rest is purely speculation right now.
Given that this is a "new generation" of super heroes, it seems as though this series will operate on its own timeline and not be connected to the one we saw in What If...? There have been multiple limited comic book series runs embracing the Marvel Zombies concept, so it's possible this upcoming animated series could be based on any one of them. One of the most widely known takes on Marvel Zombies is the five-issue limited series from writer Robert Kirkman, which was ultimately adapted for What If...?
No release date has been announced yet. Other newly announced Marvel animated projects coming to Disney+ include Spider-Man: Freshman Year and new episodes of X-Men: The Animated Series.