This is not surprising. The Trump economy has lifted all sectors of society, particularly benefiting were AAs. OTOH, Joe Biden's "you ain't black" comment appears to have alienated voters.
"In the latest John Zogby Strategies and EMI Research Solutions poll, Biden has the support of 77% of black voters while 14% back President Trump."
"In the last 20 years, only George W. Bush, running for reelection in 2004 against then Sen. John Kerry, came close with 11% of the black vote. In 2016, against Hillary Clinton, Trump won 8% of the black vote."
"In its latest White House Watch, Rasmussen Reports found that 21% of black people support Trump’s reelection. The polling outfit has found unusually high black support for Trump for several months."
https://www.washingtonexaminer.com/washington-secrets/zogby-bidens-dismal-support-from-blacks-threatens-his-election