Sure. Some people can pull that off. Doesn’t sound like OPs problem.
Also there’s a difference between over-preparing and coming in with a desperate attitude. You’re right that if you have the latter, you’re fucked. Going in with confidence, curiosity, and detachment are important too.
I find my interview anxiety is directly connected to how much sheer preparation I do. There is no substitute for this.
Spend several hours: scouring the internet for common AND uncommon interview questions. Draft strong responses to all of them. Map out your values and reasons why they are what they are. Specific professional qualities you exhibit PLUS multiple anecdotes explaining those qualities.
Then- research the damn company. Hard. Train yourself in their tone and the story they tell about themselves. WHY DO YOU WANT TO WORK FOR THEM?
Mostly importantly: Draft up thoughtful interview questions to ASK. Both general role questions and questions about the industry etc.
This takes time, and practice. But man, when you do it, you feel like a fucking boss going into an interview. And that unlocks the most important part. Mindset.
(For developers and other highly specialized roles, this isn’t exhaustive because you have steps to test your technical skills, but hopefully that helps. I gotten several jobs I’m under-qualified for by using this method)
Though it sounds like you might've overlooked two of the most important ingredients entrepreneurs need when getting something off the ground:
- vast web of influential family connections - inherited wealth
Maybe go back and try it with these two?