The way they taught is back in the old undergrad was that IQ is your capability for "learning" while your environment is basically learning to actually use and access it. In the most simplified terms.

So someone with a high IQ can be an absolute retard with the wrong environment and an eventual accumulation of trauma/baggage that keeps them from using it. But someone with a low IQ cannot overcome that disability to a meaningful extent beyond sheer force of will to "fake" it.

Like someone missing a leg can "run" with a fake leg and even appear like they might not be missing one with the right clothes. But they can't actually do leg things and are still massively crippled.