It depends on the region.
Broadly speaking, what you're describing is mostly happening because Black (and Latino) turnout was down across the board, not because the GOP was making inroads with these voters. In places like NYC and California, the GOP did make some gains with these voters.
By extension, many (formerly) black-majority rural counties in the south have flipped over the last several decades because the share of black voters in these counties dropped from a majority to a minority (for example, Baker County, GA went from 50% Black in 2000 to just 39% Black in 2020, and it flipped from D to R at the presidential level in 2016).