But even if we accept unconscious bias can be measured and has an appreciable impact on individual's behaviour, it still can't be proved or disproved in any real world scenario.
Not proved in the sense of holding up in a court trial or something. But we can get to the point where we can be reasonably sure it’s making a difference.
And just because it can’t be proved to that degree doesn’t mean we can shut down debate around it. It’s important to understand these issues as much as we can within the limits of what our learning allows us.
For instance, your assertion that the UK media have treated the Duchess of Sussex more negatively because of her race can neither be proved or disproved in any objective sense.
Well there are lots of side by side comparison to show that her actions are being judged very differently to the same/very similar actions of others.
However as I said upthread, the more difficult thing to untangle is the role that anti Americanism, anti feminism, suspicion of actors, Piers Morgan’s personal vendetta is playing in the different standards she’s being held to.