I ni ke, @Fassah !
Welcome to the Forum. Thanks for posting here.
As for your question about “mun kosan” and “o le kosan”, the expression or word that you are interested in is actually kosɔn.
As you can see from the dictionary definition (yes, the definition is from the Jula/Bambara dictionary, but the word is the exact same in Maninka), it’s a special compound postposition:
The word comes historically from ko (‘affair’) and sɔn (‘heart’).
It is typically used to express the idea of “because of” and it follows a noun. For instance:
N bada à kɛ kanin kosɔn
“I did it because of love”
(as in, “I did this nice thing for you because of my love of you”)
If you replace the noun with the question word mun (‘what’) then it can be used to say something similar to “why”. For instance:
Mun kosɔn?
“Why?”
Lit. “What because of?” or “What for?”
I hope that helps you grasp “kosɔn” and its basic usage better!
As for your specific sentence translation question, I’ve broken it off as its own topic: “The reason I don’t like X is…”