AI can help tremendously with the initial leg-up problem of shipping a working prototype -- paradoxically, if you're willing to put in the work. That is, the right kind of work: talking to people, getting suggestions, writing all your own marketing copy by hand, creating a design that has human touch, throwing it away and starting fresh (with less genAI help) when you've learned what the real demand is for, etc.
The answer is you start with the sale. Once you’ve sold it, you build it. Ideally, you sell it to customers first. Less ideally, to investors.
Most are. I’ve always been. Preörders are real.
They don’t even need much cash to change hands. Just the commitment.
Building before selling is ultimately art and hobby.