Yes. A good discussion of black immigration is Tod Hamilton's book that came out quite recently: Hamilton, T. G. Immigration and the remaking of Black America

Although Hamilton doesn't give an exact figure for the proportion of Black Americans who descend from people held in Slavery in the United States, he does say "The overwhelming majority of blacks residing in the United States descend from American slaves".

Around 10% of blacks in America are immigrants, but there would also be a few non-immigrants born to earlier black immigrants. Given that black immigration is mostly recent, (before the 1970s fewer than 2% of blacks were immigrants), and there is fairly high intermarriage between native and immigrant blacks, the number with all immigrant heritage would not be too large - although there are prominent examples of such people, like Barack Obama and Kamala Harris. These would add a few percent.

A tiny proportion of immigrants might also have ancestors who were slaves in the United States - small numbers of American blacks immigrated to places like Liberia and Haiti, so some of the immigrants from these countries might actually have American ancestry further back - but this is a small number of people.

A substantial proportion of black immigrants come from the Caribbean, and would also be descended from people who were enslaved as part of the Atlantic slave trade. So if you were asking broadly about any slave ancestry, the figure would be even higher - but I am assuming you are mostly referring to blacks who are descended from people who were slaves in the United States (based on the wording of your question). Also some Africans might also have slave ancestry, since slavery was common on the continent. And I suppose if you go far enough back everyone on Earth must have some ancestors at some point who were slaves.

So depending on your definition the figure "descended from slaves" could vary. But if I assume you mean descended from slaves living in the United States, the figure is probably somewhere a little higher than 80%. You Might be able to get a more precise figure if you can find a good estimate on the second/third generation children of black immigrants - but this might be a little tricky due to intermarriage, so it might require some demographic modeling. You can be confident though that MOST black Americans descend from people who were enslaved in the United States.