As time goes on it gets ever harder to invent 'a serious breakthrough,' wha tever exactly that means. So the percentage of lone inventors falls, but no t to zero. Many inventions are concepts rather than brute force trial, and significant concepts can still be and are still produced by single minds.
The computer is a geat example - although long in the past, it was a piece of elemental conceptual thinking that changed history. Its construction is an example of where money is required, but its invention is not.
NT