How were many people guided after they had been immoral (fasiqeen) and disbelievers (kuffar), even though Allah Almighty said that He does not guide the immoral nor the disbelievers?

No matter can occur except by the will and decree of Allah. Allah Almighty does not guide those whom He knows and wills will die as wicked transgressors or disbelievers. Rather, He guides those whom He willed to guide before their death.