أحسن الله إليكم Ustaadh, if the imam says the tasleem and a person is making du’a, should the person stop the du’a and give the tasleem or finish the du’a first?

If they will finish very quickly. Then they can finish then do the Taslim. However, they should not prolong it because what is mandatory is following the Imam. The Dua is favored and not mandatory, and that which is mandatory is given precedence.