"Nobody really knows what they're doing" is a cope that will keep you mediocre forever. There are absolutely people who know what they are doing. My advice to young folks in any field: seek out these people, and put yourself in a situation where you can learn from them. For me, it was extremely humbling to work together with far more competent engineers at Apple. Over time it transformed my mindset from "I'm pretty good at this 😎" to "I need to work harder and stop making excuses 😅"