The original series was based in a post-race society. When Kirk and Uhura kiss, it wasn’t an interracial kiss in the show because the concept of race doesn’t exist in the 24th century universe. It got backlash when it aired because some people couldn’t contemplate a the future without their current bigotry existing. Star Trek explored current social issues by visiting some planet with a veiled version of that issue.
Contrast that to Discovery where Burnham is having a conversation with an Admiral and the Admiral brings up Burnham’s family’s history of slavery.