There's no definitive answer to this question as everyone is different. Some people may find that working on their lats does make them punch harder, while others might not notice much of a difference. It ultimately comes down to trial and error to see what works best for you.
That being said, there are some benefits to building up your latissimus dorsi (lats) muscle. Stronger lats can help improve your posture, which in turn can lead to better breathing and more efficient movement. This can all contribute to a stronger punch. So if you're looking to add a little extra power behind your punches, start by working on those lats!