Can a non-developer really build a working app with AI?

Short answer

Yes for a genuinely useful class of things — internal tools, landing pages, simple SaaS products, scripts that automate a manual process. The wall is not writing the code, it is everything around it: deciding what to build, knowing when the output is subtly wrong, deploying it, keeping it secure, and fixing it when it breaks at an inconvenient moment. Those are judgement problems and AI helps with them much less than it helps with typing.