[sudosysgen]

Well, it is problem, because the assumption is that you're measuring a proxy for g that supposedly doesn't change. So if it can change, by something as simple as learning some boolean algebra, the IQ test isn't measuring what it is assumed to be measuring.

That being said, you're right that it would still be useful for measuring problem solving potential, but that's explicitly not what IQ tests are supposed to measure.

[andromeduck]

??? who assumes g can't change?

[sudosysgen]

It's generally accepted in psychometrics that general intelligence does not change in adulthood : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3950413/

I personally think it's not something that's really true, but it's how I learned it in university and seems to be the default position of experts in the field.

This is of course assuming no traumatic brain injuries or the use of psychoactive substances.