Now it could be that it is anti-black racism from a proportion of white and black officers, but maybe "white-privilege" is a better way of looking at the benefit of being white when stopped.
The problem is that there's this weird inversion where there's an assumption that such a thing must have happened to someone - it's this systemic thing that exists, so they must have experienced it. While people totally ignore the impact of "anti-racist" policies and fail to net them off.
Now, I was similarly resistant to "male privilege", but in this fight, you can clearly see it happening - even people like Douglas Murray have been forced to concede that. Even if it's not an all-pervasive thing that happens in all circumstances, it's happening here. Women are far less able to safely talk on this subject than men, due to the social expectation of "being kind", and the way that's leveraged on this subject. But a woman who's not encountered the trans issue may have never hit this in quite the same way.
So in your example, if someone has never been stopped by the police, then that instance of "white privilege" would never have occurred. Whereas they may have very definitely been hit by a "white penalty", such as explicit race-based discrimination in job/university applications.
I think you have to look at the actual impact of privilege, not just it theoretically existing. Non-colour-blind people have the privilege of being able to be pilots, for example, and this must be a huge deal to some people, but for the vast majority this "able to be a pilot" privilege really isn't relevant. Penalising non-colour-blind people generally in non-aviation circumstances for their pilot-privilege would be daft.
It's perverse to insist that someone must have a privilege when you don't know how many circumstances they've encountered where it would have occurred, AND you know you have in place concrete policies to disadvantage them.
It's perfectly possible that someone may have received far more disadvantages from systemic "anti-racism" than they've ever received relative advantages from purported societal racism. Some of this systemic discrimination is incredibly high-impact. Getting blocked from a job or university is possibly a much bigger deal than being treated better by some police once.
So "white privilege" is not a fair concept in a systemically "anti-racist" racially-discriminating environment where you hand out "black privilege". Your "anti-racism" is more concrete and measurable than the racism.
Now, fortunately that doesn't occur so much here, but in the US where a lot of this comes from, it blows my mind seeing explicitly race-discriminating organisations continue to talk as if their policies had no impact, and they weren't creating "black privilege".