It really isn’t that simple. The north didn’t have as much strict segregation but in a way it was because they didn’t have to. Economic pressure reinforced by subversive hiring practices, prejudice in housing and hostile attitudes kept black communities tight knit and localized which meant you didn’t have to have specific “Colored schools” because they were created by these forces squeezing folks together into controllable blocks of population.
In the South the fall of segregation had a number of nasty fallouts which harmed black communities as well. When they merged the systems there was a historicly significant loss of black teachers. People got up in arms over really stupid questions like “What if my menstruating daughter had a black male teacher” and that prejudice ensured that a lot of the teachers who understood the challenges of being black in America were no longer in a position to help students.
This meant that effectively in the North segregated schooling continued to be a thing in practice but not in name while in the South it wiped out infrastructure that was helping black students succeed. It was handled incredibly poorly and was not unambiguously good but it did change a lot of the legal categorizations and is considered a win.
I mean when you look at Harry Potter through a magnifying glass it’s actually very pro status quo with a lot of issues breaking down to “the wrong people in charge” a lot of gestures made towards the sort of social problems of the society… Like look at house elves. We meet Dobby and everyone agrees that slave holding situation isn’t ideal but once we meet more house elves we learn that Dobby is kind of a weirdo and that they are effectively a sentient slave race with only exceptions like Dobby taking issue with being bound. Hermione sees this as a legitimate issue as any potential elf could be a Dobby but then great detail is placed about how annoying and virtually pointless her advocacy is but the rest of her society and the framing effectively informs the reader - “don’t think about house elves. Dobby is fine. It’s not your problem and shouldn’t be.” It’s framed as a problem to be solved on a small scale interpersonal basis because by and large the system works.
It’s generally difficult for people to critically read a narrative that throws up that many hairpin bends particularly when the set ups are made in the book that these things are social problems… but then never paid off. That it happens a fair amount innthe books is a fairly confusing yarnball. It feels progressive in the same way a company mission statement that is not being enacted in any real way feels progressive.