They may be in for a cruel surprise. In most African countries, tribalism is far worse than "racism" in America with far less protection against discrimination. American "blacks" for the most part have no tribal identity and will face being "othered"... in many countries they will be called "colored" (a term used to describe people of mixed race in many African countries).
My comments are based on my talks with many people from Africa including my black daughter in law (from Zimbadwe) and former son in law (from Nigeria). Over the past five decades I have had many conversations with Africans from all parts of Africa and the resounding comments match with the comments in the link below.
https://www.crsp.pitt.edu/op-ed-racism-across-world-tribalism-africa
Those conversations as well as the teachings of MLK have convinced me that what we call racism is a form of tribalism based on skin color. The goal of a diverse society like the US has to be integration, not separatism. Africa is far less diverse and so rather than integration being a goal, the majority often feel very comfortable discriminating against minorities. This is a serious issue in South Africa, Nigeria, and other African nations.
Separatism is catching hold in America where progressive liberalism has embraced identity politics as a tool of division in order to gain power.
More and more everyone "identifies as being a member of this tribe or that".
Separatism is divisive and ultimately produces bigotry. When that bigotry is based on skin color, we call it racism. But we have religious bigotry like antisemitism and Islamophobia, we have gender bigotry, if there is a way to be bigoted, we have it in America.
Rather than being frowned upon, it is being embraced by the "woke movement" by ascribing some bigoted behaviors as okay like the recent attacks on October 7 by Hamas against Jewish women and children. We should be condemning all bigoted behaviors as wrong, not picking and choosing which ones are okay.
I hope those Black Americans that move to Africa to escape US racism find what they are looking for. In the end, the "pursuit of happiness" is a fundamental unalienable right" of all humans. If they fail, perhaps they will return and continue the fight to end "separatism/tribalism" and promote integration in America. We are far from perfect, but thanks to MLK and others, the importance of integration is clear even if securing that goal may take generations.