T'Challa named his ship the Mandela after Nelson Mandela instead of the Milano which Peter Quill named after Alyssa Milano.
Though Chadwick Boseman's final live action performance was in Ma Rainey's Black Bottom (2020), this is Chadwick Boseman's true final performance. Filming for "Ma Rainey" wrapped in August 2019 which was the same month that "Marvel's What If?" was beginning to record its voice actors. Chadwick Boseman passed on August 28th 2020.
In The Making of What If...? (2021), executive producer Brad Winderbaum reveals that Karen Gillan came up with the idea that her character Nebula would refer to T'Challa as "Cha Cha" on the day she recorded her lines.
Djimon Hounsou who reprises his role of Korath from the Marvel Cinematic Universe, also provided the voice of T'Challa in the animated series Black Panther (2010).
Groot can be seen in silhouette inside one of the Collector's pods.