A child of 3 years does not speak sentences

Hello! My son is 3 years and 2 months old. He does not speak sentences, for example, if I ask him what he did in the garden, he will simply answer me nothing. My son knows animals, what sounds they pronounce, simple geometric shapes, colors, counts to 10, knows all the letters, but he absolutely does not communicate with us, I will not hear an answer to almost any question. The teacher in the garden says that he does not play with the children on his own, but I personally see interest in games with children on the playground when they come to visit us with children. A neurologist diagnosed attention deficit hyperactivity disorder, but I disagree with this diagnosis. How can one develop speech? How to encourage a child to dialogue?