Never.
A primarily "Mohammadean" land in the scorching desert where by and large anti-blackness was rife and the limitations of southern agriculture are pushed to the very edge would not be a destination most American blacks would go to.
For better or worse the narratives of Robert Adams a 19th century mixed race man claiming to have been enslaved in the region would have turned most off.
While yes slavers did exist in Liberia to sell to foreigners it was not in the interest of freed and free American blacks to risk raiding after leaving the U.S.
Now if the question was the Moroccan sultan calling on the U.S. to free all "Moorish Slaves" (taking one step further beyond the Sundry Act) then yes, a mostly Fula/Peul migration of largely literate and former elite men and women could and probably would settle down.
Say some 100-400 tops.
I still say Southern and Central Namibia is best.
Milder than the Sahara, filled with Euro-African cultured and mixed race Oorlams already conquering Nama, Basters arriving, limited European presence, vast Whaling potential suitable for the many free Whalers, sailors and captains of the Northeast some of whom spoke Dutch along with Fula and Sahelian pastoralists in Texas, Louisiana and elsewhere in the South; as a bonus a close proximity to Christian Capetown?
it's the best bet.
