Does neutering stop a male cat from developing cheek jowls?

Yes, neutering will stop a cat from developing cheek jowls, because the jowls are a secondary sexual trait of male cats. After neutering, testosterone drops, so the cat naturally stops filling out its cheeks.

If you want your cat to develop jowls, build up his nutrition before neutering by feeding more protein-rich foods like beef, chicken breast, and egg yolk, and only consider neutering after he has filled out. After neutering, do not keep feeding large amounts, or he may become obese, which harms his health.