I think he is sincere. Hear me out, a lot of people are skeptical because last times they had a summit in 2000 and 2007 nothing came out of it. Here’s the difference. Kim Jong Un is NOT his father. Even when he spoke, he had a noticeable Swiss-influenced accent that not a typical North Korean accent.
He willingly admitted that North Korea’s infrastructure is really bad, something that his father never admitted to. All the news seems to indicate he is well aware that South Korea is far ahead of his country and that his country is impoverished. He is also aware that continuing to pursue nuclear weapons and/or reneging on the agreement will result in suicide for his regime.
Let’s not also forget , that unlike his father, he visited South Korea for the summit. Previously, all summits were held in Pyongyang. He even told President Moon that he would like to visit Seoul sometimes. He seems appreciative of the Kpop singers (especially Red Velvet) that were sent to him.
All information seems to indicate he was playing up the ‘madman’ act in order to consolidate his power in North Korea, but does genuinely want to make progress as long as his regime’s safety is ensured. He even visited the Chinese tourists who were injured in the bus accident and apologized to the Chinese embassy, even though he had no obligation to do that. The actors have changed. I don’t believe he is the same as his father, and his actions seem to differ as well.