You can get smarter by reading and people should be told that.
I'm really interested in this because I have someone who keeps telling me this isn't possible. Do you have a source by any chance?
Intelligence as an aggregate term refers to a number of things which include but aren't limited to verbal acuity, spatial reasoning, abstract reasoning etc and the individual components differ from person to person. So you might be amazing at abstract reasoning and your friend might have above average verbal acuity.
I agree with the notion of intelligence being a social process. I think IQ isn't able to capture that all. Though that is not individual intelligence, it is collective intelligence but individual intelligence is a function of genetics+non-shared environment+collective intelligence is what I want to say.
You can see collective intelligence at work if you examine language. Certain concepts have a high power:weight ratio and can help you make better decisions than you otherwise would and those concepts first have to be discovered and then they have to diffuse throughout the general population and that happens via language.
I think the '80/20' or Pareto Principle is a fantastic example of this. It's very widely known and it helps you reason better about the world in a useful way. Before that was ever discovered, nobody could leverage it. As time ticks by our models of the world are slowly getting higher and higher resolution (if that makes sense as a metaphor) and that is filtering down into the general population.
Reading is fantastic. You can acquire in 4 days what it took someone 40 years to come to. I think regardless of your IQ the more data and the higher quality you can assimilate you can increase the resolution of your models of the world and that helps you reason about things more clearly.
I'm always really fascinated by people with learning disabilities who really buck the trend and go on to do amazing things academically. Sometimes the strategies they come up with for learning are unbelievable either in terms of creativity or sheer determination. There are some pretty extreme examples of this in Dr Norman Doige's The Brain That Changes Itself and a favorite recent example I encountered was David Goggins' talking about how it would take him 18 months to get through the textbook for his diving training, so he started memorizing it 18 months ahead of time by writing out every sentence in the book by hand 10 times each. I swear there is a tonne of unutilized headroom in the general intelligence of all populations.
I'm pretty optimistic about the general trend overall and I don't think having a low IQ in a general population or even as an individual necessarily consigns you to a life of mediocrity or that you will be unproductive as a society.