How to handle requests for a race-based exam structure?
I would suggest offering something in response that makes the students feel like their concerns are heard, without compromising the academics of the course.
For example:

I understand that this is a difficult time, especially for minority students. Unfortunately, if I cancel the final exam, I won't be able to assign a grade to these students and they won't get credit for their work this semester. But in recognition of the extra challenges some students are facing right now, I am going to schedule an additional review session and office hours before the final exam. This way, students who are struggling can get additional opportunities to master the material before the exam.

A response that communicates empathy and understanding is much less likely to develop into a PR disaster than one that is irritated, defensive, or dismissive.