Depends on how you put in the data.

If you do it all at once it’s trivially easy. They know a person doesn’t just become a new person overnight.

If you commit to creating an elaborate fake personality by doing things your fake self would do, it can be harder, but not impossible. Certainly not a problem for some of the greatest minds in Silicon Valley.

Meh...the whole "Silicon Valley genius" trope is another myth that needs to die. Being able to code a depth first search doesn't make anyone a 'genius' and there are limits to what AI can do even with bushel baskets full of data.

For many years Facebook thought I was Jewish and was spamming me with ads to become a rabbi and move to Israel, but I am the least Jewish person you'd ever meet. And that could easily be determined by publicly searchable data about myself.

I've faked my phone number for about two weeks on Android when I installed their app to try it. 3 years after, they still ask me if my number is some random Italian number, I'm not sure they have that many checks in place.