> It's generally true though

I agree, but that isn't what mathieuh wrote. I'd say racism against white people is less common and generally less impactful, but it isn't impossible or inevitably different.

> since Whites tend to be a smaller majority

You're underestimating the diversity of the United States. There are many places in the US where white non-Hispanic Christians are a minority. In fact, white non-Hispanic (but including Jewish and Muslim) people are only 60% of the population of the US.

Yeah the harm is going to vary by location and situation within the US, but it also goes beyond just demographics. It's also about the social constructs operating in a culture. A White minority in Singapore doesn't face much racism and the racism they do face isn't damaging because they have a wealthy, powerful community or embassy to fall back on. But if you're a Bangladeshi worker with no rights the situation is totally different almost 100% of the time with no exceptions, you could get beaten up by your boss and literally nobody cares. The locals and police doesn't care, there is no embassy or media ecosystem of a rich country to care, and so on. It's direct racism and the end products of racism top to bottom.

This is what people are trying to point out when they talk about Whiteness. They're talking about the construct that it's good and default to be White (or Han if you live in China or Japanese if you live in Japan) and this construct can even hold true in places with a White minority (e.g., how White people get treated in Singapore, or colorism culture in non-White countries).

That having being said, White people as individuals are empirically the least racist people. That's just empirically true according to survey data. But this is largely besides the point that was being made above.