You're not looking for a "startup" you're looking for a "company".

Go and find an established company with a product and customers and help them maintain or maybe grow their business. Find a post-IPO or post-acquisition company that isn't trying to hustle or pivot or disrupt and get a nine-to-five where you can punch the clock and collect a paycheck and everyone's happy.

Startups are not for everyone. Don't be afraid of working somewhere that already figured things out and is only executing on that plan.