Not that I think this is _particularly_ relevant (as mentioned elsewhere, most of the characters aren't even _human_, and it's not like he generally specified "but if they _were_ humans, the Ringwraiths would definitely be white"), but LoTR was finished in 1949. There were lots of non-white people in the UK in 1949; if you've heard of the Windrush scandal, the people impacted by that arrived the year before, and it's not like they were the first non-white people in the UK...
I agree that this would be extremely hamfisted. Especially considering the books already have some metaphors for racism like the strained relationship between elves and dwarves. However, I also think this kind of a thing is just a symptom of bad writing - not some woke conspiracy.
Also, I think most aren't actually opposed to minorities being in the show, but rather the hamfisted way they think theyll be included with. (I personally expect racism being a big part of the show that will need to be fought.)