The problem with people who have slave ancestors is that they have no real idea of where they came from short of getting their DNA sequenced: and I'm sure the results would be shocking. That's because the places the slave ships originated were ports where the slaves were brought from the interior for trans-shipment. I'm a Euro-Mutt according to my DNA so pretty much everywhere in Europe, except the Iberian peninsula can be considered my "roots". In fact, I can't really name a country for a good part of my continental ancestors: only my maternal grandmother's ancestors came from countries (France and Germany). The maternal grandfather were from before the US became independent, so it would be something like Holy Roman Empire or Hanseatic League for the ones who weren't British.
Now, the problem with Africa is that there are lots of different cultures and most blacks who came as slaves came from the West of Africa. So, what to do: create a holiday based on what you believe might be your traditions.
Kwanzaa comes from Swahili, which is an East African language. Swahili is a combination of Bantu, Arabic, and Portugese. These people are too infatuated with Julius Nyerere to realize that Swahili is pretty much a creation of the Arabic Slave trade...
Odunde is probably the better choice if you gotta choose since it is based upon the Yoruba traditions. [1] Yorubas may be one of the largest ethnic groups in Africa, but.
The ethnic groups of Africa number in the thousands, with each population generally having its own language (or dialect of a language) and culture. The ethnolinguistic groups include various Afroasiatic, Khoisan, Niger-Congo and Nilo-Saharan populations.
That's about like me saying I feel most European when I identify as Kosovan (not to denigrate Kosovars, but that was what came to mind. And I don't particularly feel Kosovan. For that matter, I don't feel particularly German or Eastern European either). I'm a Euro-mutt, but some traditions I have a connection to leave me cold, but since I'm pretty much everything from East of the Iberian Peninsula to West of sort of a line through the Scandanavia, Baltic States, and Poland down to Turkey: I've got a lot of Latitude.,..
But when you don't feel a heritage: go for it.
Then comes JUNETEENTH which is pretty much an obscure event that received a huge build up in 2020 to become forgotten again. While having to do with former American Slaves, it would probably be a good candidate for a holiday. The unfortunate thing is that it only deals with a small population of slaves in Galveston, TX who were told not only had the Civil War ended, but they had supposedly been free for a few years. But celebrating like is like celebrating the end of World War II on the date the Last Japanese soldier holing up waiting for the glorious troops to return.
Then again, the US does have this habit of making events that happened after the war ended into a big thing, such as the Battle of New Orleans.
The big issue here is that these events are small things even though there is a rich set of traditions for whatever you want to call this heritage.[2] Kwanzaa has been built up, but I have yet to meet someone who seriously celebrates it other than my ultra liberal Jewish cousin. Get me somebody who is black who celebrates it! I don't know about "African-Americans", but this set of holidays leaves me dry.
I'm pretty sure there must be something out there that could form a holiday and unify black people, but these three aren't great candidates. The problem is that like Europeans, Africans are pretty diverse. Actually, they've got us European beat by a lot in the ethnic diversity department. It's just that the colonisers changed the map to make the nations that now make up Africa. It's like me trying to classify my ancestors who came from what is now a diverse set of European countries.[3]
[1] Toss in we have moved from East Coast Slave Trade to West Coast Slave Trade.
[2] There is a lot of European in the former slave population gene pool, plus not all people of African descent have slave heritage, and so on.
[3] It's slightly easier for me to choose ethnicity since there are a few "centres of gravity", altough at least one of them (Rhineland) has been up for grabs for ages. But even British is up for grabs with not only English, but Welsh, Scots, and Cornish...And that's just a start.