Sad to hear about racism on Nextdoor, but I am not surprised. I am an admin (Nextdoor calls this a "lead") on my neighborhood's Nextdoor and I have seen and promptly deleted several racist posts over the year that I have been an admin. It is up to the admins to apply the rules for their neighborhoods. If you can prove that your admins are passive and not enforcing Nextdoor's rules, they will act and remove lead privileges from the bad admins.