I would argue that Rainman (1988) being a lot of people's first introduction to autism propped up the autistic savant trope

Hackers (1995) did not reflect reality at all, and entirely made up a look, sound and feel of hacker culture for the film. Tech press largely panned it as rediculous, unrealistic and innaccurate, but hacker culture actually morphed into something close to what was depicted in that film because it's honestly way cooler and way better than what the actual hacker culture was at the time

Others have already pointed out really good examples like Upton Sinclair's book The Jungle which spawned a lot of food safety laws, or Wargames (1983) basically prompting the Computer Fraud and Abuse Act

Edit to add: I also remembered another very influenctial author at the turn of the century was Henry George who wrote a now under-discussed book called Progress and Poverty which is widely credited for triggering the beginning of the Progressive Era

In a similar vein, Charles Darwin's On the Origin of Species basically kicked off the entire field of biology with the scientific theory of evolution