The primary qualification for being regarded as an intellectual is to develop a reputation and convince people to regard you as an intellectual.
Being widely regarded as “intellectual” is a social status. It is achieved through specific types of social climbing.
Social climbing and reason are enemies. They’re incompatible. Someone really good at reason would reject social climbing. So we should expect to find that most “intellectuals” are bad at reason. And, from extensive surveying, I think the evidence fits the prediction well.
Being regarded as an intellectual does have something to do with being smart or figuring out some good ideas, at least in some cases. It’s not purely a social game. The best thinkers sometimes gain some intellectual reputation, though often not the best or highest reputation. So e.g. the best living economist, George Reisman, is largely unheard of, but would be regarded by most people as being an intellectual (since he was a professor and wrote a 1000 page book on economics). There are many more examples of great thinkers without accurate reputations.
Some types of intellectual accomplishments are easier to judge than others, so they do a better job of leading to a reputation regardless of what else the person does. Generally scientific ideas (“hard” sciences only) are easier to judge than philosophical ideas. Hence most famous philosophers are awful, while a fair amount of famous scientists are actually good (particularly people who got famous for scientific work, not for writing popular books about science or doing a science podcast or something like that).
Reputations sometimes get more accurate centuries after someone dies. That removes some of the social factors from mattering, and it gives people in the field more time to sort out which ideas are actually good. In general, scientists are much better at science 300 years later, so they can do a decent job of judging the scientific achievements of the scientists from 300 years in the past. However, historians are often wrong. The news is often wrong about what happened yesterday, and historians have a much harder job that gets harder as things get older. False reputations can persist for centuries and the refuting information can be lost.
The good news is: making intellectual contributions has a lower barrier to entry than you may have thought. You don’t need a fancy reputation. Most of the people you think are above you are incompetent. You don’t need the same education or peers that they have in order to do good work.
But beware. You can easily make the same mistakes as them. You can focus on social climbing while pretending to yourself that you’re seeking truth. Avoiding that is more important, and harder to come by, than any credentials.
The bad news is: if you don’t think, you can’t safely expect other people to do it for you. It’s not a safe thing to count on others doing correctly. You should try to learn and reason, yourself, if you value your life, instead of leaving your fate in the hands of our society's “intellectual authorities”.
The world needs more people who are willing to try to learn and think. The main tools needed are honesty, curiosity, energy, avoiding bias, choosing truth over social perceptions, and some stuff like that, not to have an extensive education or to be born a “genius”. Those things are harder and rarer than most people think, but if you think you have them, do something with them. E.g. start discussing ideas in the comments below. Anyone can do it if they are willing to prioritize truth over social status.