Honestly, Liberia is the short answer to this question. There would be a new black ethnic group embedded into whatever existing ethnic conflicts those countries were engaged in before the arrival of fba/ados. Best case scenario would be a caste system with ados/fba at the top. Obviously this wouldnt bode well with the existing population.
Additionally, this would also mean that black brits would be the most influential black people because they would be the closest to white wealth/resources. Black canadians would be second place. Their 2 cultures would dominate global black thought because they could be signal boosted by the brittish equivalent of warner brothers, motown records, and viacom.
Looking back historically, i think world events wouldve transpired the same except that south africa would probably still be running an apartheid state in 2022 similar to how Israel is currently doing to Palestinians. That was primarily an ADOS push, so south africans would suffer from ados/fba repatriation.
Finally, you would lose a lot of novel inventions that fba/ados developed because of their experiences in post slavery life. For example i think a world where fba/ados return to black nations would not have peanut butter, peanut oils, glycerine-vinegar, etc from George Carver who was a prior slave studying the plants of his region. Same could be said for Sarah Breedlove (CJ walker) who had to invent black hair care products in a white American environment that was bereft of them. But i think this would only be true for inventions which were based on the specific experience and environment of fba/ados. For instance, i think Latimer's carbon filament and a lot of granville's telegram inventions wouldve still been invented because may people outside of fba/ados were working in tandem on them.