Unless you're doing something fabulously unique (at which point I'm jealous you get to work on such a thing), they're pretty good at cribbing the design of things if it's something that's been well documented online (canonically, a CRUD SaaS app, with minor UI modification to support your chosen niche).

And if you are doing something fabulously unique, the LLM can still write all the code around it, likely help with many of the components, give you at least a first pass at tests, and enable rapid, meaningful refactors after each feature PR.