African-American voters are certainly perfectly comfortable with "socialism" (There was a survey several years back that showed they were more comfortable with it than other groups). So, progressive/socialist policies were definitely not the problem. My disagreement with the op-ed is that it understates the way that Bernie's brand of progressivism intentionally and vigorously excludes marginalized experiences that have nothing to do with class.
There is a reason he didn't listen to his African-American organizers. There is a reason his campaign rejected the overtures of African-American political and civil rights leaders in 2016. There is a reason he uses "identity politics" as a dog whistle. It was not just an oversight or bad strategy. His strategy is to focus on class, to the exclusion of all else. It is explicitly class-inequality first messaging. Connecting with African-American voters threatens that myopic worldview. His strategy was and is to win without the African-American vote because he did not want to accommodate experiences that are not rooted in class inequality. That didn't work out too well. He's not only lost African-American voters to Biden but also women.
The racist and misogynistic underbelly of his campaign is a direct result of this strategy. Someone wrote an article recently calling the progressive left a white male movement. It's not true, but Bernie's politics certainly makes it seem so. I have hope that people like AOC see this failure, take a lesson from it, and shift the progressive movement in a direction that allows it to build a broad coalition.