Where I live the government literally built a useless freeway just to separate poor black communities from the middle class white ones. This is actually very common.

You imply people make their identity around race and thus choose to be separate because they are only comfortable in their culture, but you have the causality the wrong way around. People for the most part don't make their race their whole identity and voluntarily separate their communities based on that - most people actually seem keen on interacting and sharing culture and space, but there are racist policies still that keep people segregated and create dramatically different lived realities among populations. These racist policies physically separate people, and the economic impacts keep the disadvantaged folk stuck in ghettos and make it hard to integrate into more affluent "white" and mixed spaces.

Black folks are treated differently by the police, by educators, by employers, and this translates to different economic, health, and political outcomes for many people of color (tbh viewing this as "black" and "white" is not how race works in the U.S., it's more like "white" and "not white" with a spectrum and some inconsistency based on how "white passing" some in-between people are).

Not to mention that property taxes are what fund local schools and infrastructure, so if you live in a more affluent "white" neighborhood you have better funded schools and are more likely to go to college, get a good job, afford a home, etc. and growing up in a poor neighborhood means your schools are not as well funded and the opportunities available to you are limited.

Not really adding, it's just a comment on the topic: I've always been confused by mass media saying Kamala Harris is black. There seems to be something about her physical features that mark her "black" in the eye of US Americans.

While racism is probably different in S American countries like Brazil, I don't for one second believe it no longer exists there.

One, because I've met Brazilians and read the news about Brazil and consumed Brazilian media. Two, there is still a strong correlation between race and class, https://en.m.wikipedia.org/wiki/Racism_in_Brazil, see the section on Persisting Inequality.

Centuries of slavery, followed by another century of segregation, and nowadays we have one of the most racist countries in the world.

Decades of inofficial segregation that is being enforced by zoning, landlords, prices, corrupt officials, CIA drug campaigns, etc

Basically slums. If you physically seperate groups of people, they will always see the other as different and eventually develop distinct cultures, dialects, etc. which only furthers the social seperation.