There is of course always more to add, but there have been previous answers about this: see /u/tropical_chancer's answer in The Arabs and the Ottomans enslaved millions of black Africans. Where are the slaves' descendants now?, and several of the answers in the thread Why is their a relatively small African diaspora population in the Middle East despite the fact that the Arab slave trade brought millions of Black slaves from Africa to the Arab world for more than a thousand years?, perhaps particularly those from /u/textandtrowel and /u/yodatsracist.

I would say the tl;dr is that 1) there are still sizeable black minority populations in many parts of the Middle East; and 2) descendants of Africans enslaved in the Middle East can be less visible than an American might expect due to lack of stigma around intermarriage.

(Incidentally, mods might want to consider adding this to the FAQ, since it's asked here semi-frequently.)