10x engineers definitely exist. Know a few and have hired a few. They are not 10x compared to anyone ever, but generally 10x to their currently aged or experienced peers.

They learn for fun. They are endlessly curious. They are incredibly humble and get things done.

They do get more done in their part time hours in the evenings than a full time equivalent. More importantly, 10x really helps with building the quick things quickly and growing them as quickly as possible.