You are correct in alluding to the fact that there are groups such as the Black Hebrew Israelites who are extremely concerned with identifying who the “real Jews” are.
I do not believe you are correct in asserting that either the BHI’s opinion on this issue nor the mainstream Jewish response would be barred from discussion here according to the “no challenging identities, even by implication” pseudo-rule. For many reasons, including the fact that discussions of who is or is not a Jew have in fact happened here for decades including long after the huge focus on trans issues began, and have not, in fact, been curtailed by any such rule.