I keep seeing two completely opposite takes on this. One side says IQ is basically determined by your DNA and environment barely matters once you control for it properly. The other side says intelligence is mostly shaped by education, nutrition, and socioeconomic factors and that genetic determinism is just pseudoscience with a bad history. What does the actual current evidence say and how confident should we be in the heritability estimates that get thrown around?
The consensus among researchers who actually study this is stronger than the public debate suggests. Twin studies find heritability estimates between 50 and 80 percent in adulthood. Adoption studies converge on similar conclusions, with adopted children showing IQ correlations with biological parents that strengthen over time while correlations with adoptive parents fade toward zero. Modern molecular genetics corroborates this directly. Genome wide association studies identify thousands of variants that collectively predict cognitive ability, and within family sibling designs show these effects are largely direct rather than mediated by socioeconomic confounds. The ancient DNA research from Reichs lab found intelligence polygenic scores under positive selection for thousands of years, which is hard to explain if genes were not doing meaningful causal work.
The adoption fadeout is the finding that shifts most peoples priors when they actually engage with it 
If shared family environment were the dominant force you would expect adoptees to resemble their adoptive parents more over time. The fact that the opposite happens is really hard to explain without substantial genetic influence.