I haven’t watched even close to all of Dr. Who. Mainly David Tennant, Matt Smith, Peter Capaldi and the guy who came before David Tennant, whatever his name was.
Haven’t gotten to Jodie Whittaker yet, mainly because Peter Capaldi’s seasons were such snoozefests to me that I stopped watching.
But anyway, it seems The Doctor is capable of reincarnating in any kind of body and doesn’t know which one is coming next, often to hilarious effect. Inhabiting a black or a female body would be totally expected by this point, and there’s nothing in canon to my knowledge that would prohibit it.
The freak-out by some “fans” over the fact of a black or a female doctor is so strange to me. “Fans” in quotes because they haven’t offered much of anything in terms of knowledge of the series to prove they are real fans. Just finding a casting choice to rage at for their own purposes.
And look, if you think Jodie Whittaker or the new guy are bad actors or the writing in their seasons sucked then that’s totally valid… but raging at the series for casting a female doctor period is the textbook definition of sexism.