It is always a bit difficult to assess from a picture, it’s way better to feel the rabbit over. I think I see a dewlap tendency under his chin (although on the pics it’s spread out so it rests on his “shoulders”. If it is a dewlap you can feel it, it’s like a pouch with soft and squishy contents.
If that is the case with your bun, it is a sign that he is overweight. Male buns shouldn’t have dewlaps. Unspayed adult female rabbits tend to get dewlaps even if they’re not overweight, and the dewlap may or may not go away after spaying. The dewlap on a doe is often firmer and looks somewhat like an Elizabethan collar.
Desexed rabbits can however develop physical traits that are similar to what’s commonly seen in the opposite sex.
I’d tentatively say he may be a bit on the plump side and might benefit from a slow tapering down of his daily pellet ration, which hopefully will encourage him to eat more hay. (Hay is, as you know, the ideal bun food!)
He does look very happy and relaxed though 🙂