Yes, the UK is racist. It has to be because every single person is a product of their upbringing and history and so comes with preformed ideas about other people. In short, I think all of us have some element of racism. And sexism. And ageism. Prejudice is rife in all peoples.
One of the side effects of the press being controlled by middle aged white men is that they get a greater voice for their prejudices. Their coverage is racist. It is sexist. It can also be ageist. And their targets tend to be people unlike themselves. It would be hard to think "straight outa compton" or "niggling" was anything other than thinly veiled racism tbh.
MM is mixed heritage so takes the racist flack. She is a woman and so takes the sexist flack (see how she is held responsible for Harry's behaviour).
Some people don't like her because of her black heritage. Some people don't like her because she's American. Some because she's a woman. Some because they don't like her actions, such as the SA interview. Some for a mixture of these reasons.
For many, the reasons why are hard to unpick. Why do people find gentle and calm Kate to be good - perhaps because we have a prebuilt template that those features (typially the features desired in white, upper class wives) to be good? Why do people struggle with bold and outspoken Meghan? Perhaps because those features have typically been undesired in women and people of colour because it makes us harder to control? So they have seeped, unbidden, into a societal template of what makes a good royal woman and what makes a bad one.
See also, how the template of a succesful business man seeps into our perceptions of who is good at their job and who isn't. We see smart dressed people who speak loudly and with confidence as being good at many jobs for which those attributes are not really the right tests of performance. Man typically get easier performance ratings than women - more often given the benefit of the doubt. This then happens even more so for people of colour (especially women) if they are in positions of power.
I don't know whether I like Meghan or not - and I don't know to what extent my opinion on her is affected by my own prejudices. But I can see that she was always in an impossible position because there is no person on which she could have modelled her approach to royal life.
If she acted exactly like Kate and was quiet, observant, shy then this would have been totally at odds with her stage in life (i.e. much older than Kate was when she started in the firm) and her background, incuding her Amrican upbringing. An abandonment of who she was.
So she acted like she is, confident, bold, outspoken and in this has been compared unfavourably to Kate and to the our template of royal women.
An impossible choice, regardless of her intentions.