Boston's black population is declining and isn't a quarter black anymore. The '23 ACS estimates that Boston is 18.9% black alone:
Census data for Boston, MA (pop. 652,442), including age, race, sex, income, poverty, marital status, education and more.
censusreporter.org
Most large, major cities, have a large population of "mixed" blacks---blacks mixed with a nonblack---, that take the total black population up 12-13%. So in theory, Boston's total black population is around ~21.2%. All that said, that's a LOT of black people and I've been to Boston twice (most recently December '23), you see black people there. We are very visible...
The problem is Boston is very culturally white, which is to blame for tge mainstream images we get of Boston...