The Youtube channel Extra Credits released an episode on the Mali Empire (https://www.youtube.com/watch?v=UkayShPilkw), at the end of which they mention that King (Emperor?) Mansa Abubakari Kieta II sent ships into an Atlantic expedition where they found "A river flowing through the ocean".
Is there evidence of Mali exploration/colonization of South America, which seems within the realm of possible given its relatively close geographic distance to Brazil?
Mansa is a military title, originally meaning something like "supreme commander" but evolving to have connotations making it similar to a royal title. So, calling him "Emperor Mansa" is a bit redundant.
To answer your question, no, there is not evidence to suggest that a Malian fleet reached the Americas. In fact, the origins of this story come from a Syrian historian named Shihab al Umari who was chronicling the Hajj of Musa Keita to Cairo and to Mecca. Musa's hajj happened circa 1324, and al Umari conducted the interviews about Musa's time in Cairo 12 years later, but may not have written down his account until perhaps 20 years after the fact (i.e. the mid 1340s).
This is important because, Abubakari II is first mentioned in al-Umari's account, and the story of the overseas expedition is introduced.
I wrote a bit more about the recent history of this myth here and talked a bit more about al-Umari's account of Musa's hajj and the historical value of it here
There is always room for discussion, but perhaps the section Travel and contact across the Atlantic and Pacific before Columbus from our FAQ will answer your inquiry.