Exactly. I was looking at this 2016 article about him and apparently he did out-and-out laugh once.
"Thanks to the power of the internet, there is proof that our president has indeed laughed at least once. This was during a campaign rally in January, when Mr. Trump’s speech was interrupted by a barking dog.
“It’s Hillary!” an audience member shouted. And the candidate tilted his head back, opened his mouth wide and laughed without reservation, quite possibly for the first time in his political life."
Humor is a policy tool that leaders from both parties deploy. But not Trump.
www.nytimes.com