Nurture v Nature is complicated (and thus so is heritability, which can change with the environment). Yes, if you lock someone in a dark room for their whole life and never speak to them, their resulting IQ will be entirely the result of environment.
That said, malnutrition isn't a thing anymore: Too much nutrition is the problem for our lower classes. Whatever portion of the Flynn effect that had to do with malnutrition ended decades ago (along with the Flynn effect itself).
Adopted twin studies show quite clearly that IQ is strongly hereditary in the conditions of modern western society. The IQ of a child adopted into an upper class home is better predicted by the IQ of their birth parent than they are of their adopted parents. There might be environmental detriments that lower the heritability of IQ at the lowest end of SES, but that is extremely questionable (Eric Turkheimer vs Alt Hype: https://www.altcensored.com/watch?v=WPV6Hz9iwQo)
It is possible that wearing a mask and lockdowns will stunt the IQ of children, as it is massive systemic abuse on a large scale. However, most interventions that have an impact on the IQ of children only have short-term effects. IQ's heritability increases with age, peaking in the early twenties at around ~70%. Hopefully, this applies to temporary negative interventions as well.
Nurture v Nature is complicated (and thus so is heritability, which can change with the environment). Yes, if you lock someone in a dark room for their whole life and never speak to them, their resulting IQ will be entirely the result of environment.
That said, malnutrition isn't a thing anymore: Too much nutrition is the problem for our lower classes. Whatever portion of the Flynn effect that had to do with malnutrition ended decades ago (along with the Flynn effect itself).
Adopted twin studies show quite clearly that IQ is strongly hereditary in the conditions of modern western society. The IQ of a child adopted into an upper class home is better predicted by the IQ of their birth parent than they are of their adopted parents. There might be evironmental effects that lower the heritability of IQ at the lowest end of SES, but that is extremely questionable (Eric Turkheimer vs Alt Hype: https://www.altcensored.com/watch?v=WPV6Hz9iwQo)
It is possible that wearing a mask and lockdowns will stunt the IQ of children, as it is massive systemic abuse on a large scale. However, most interventions that have an impact on the IQ of children only have short-term effects. IQ's heritability increases with age, peaking in the early twenties at around ~70%. Hopefully, this applies to temporary negative interventions as well.