Yes, generally referring to groups of people as pluralized adjectives is considered dehumanizing.

Note that Blacks and the Blacks are both considered offensive and should not be used. Black people is the preferred plural form of Black.

https://www.archives.gov/research/catalog/lcdrg/appendix/black-person

[A]im to use Black as an adjective, not a noun. Also, when describing a group, use Black people instead of just “Blacks.”

https://nabjonline.org/news-media-center/styleguide/#styleguidea

This is for the exact same reason you would not refer to a singular Black person as “a black”. If you still have trouble perceiving the issue, consider how jarring the term “a gay” would seem in print.