https://en.wikipedia.org/wiki/Flynn_effect (tests are re-standardized to keep the mean at 100, but the un-standardized mean actually increases over time)

then doesn't this counter the argument that IQs are falling

It does. They are not. Or at least if some factors are lowering it, other factors like better nutrition and deleading etc. are more than counteracting it.

You would still have outliers that raise the mean - mostly children from wealthy people who can afford to raise their children on rural-ish areas, away from environmental pollution (not just lead, but also particulate matter dust/NOx from roads, industrial airborne toxins, and noise).

There aren't enough people so rich that they can live in country estates and remote coastal "summer" residences all year (so, neither parent has a job they need to be at) while sending their kids to rural boarding schools to show up in those stats, I expect. Plus you may have trouble pinning down where they actually live most of the time, even if you tried to account for them.

Beyond that, given rural areas have been subject to over a century of severe brain-drain and intelligence is fairly heritable, I'd expect that to overwhelm any benefits of country living, if you tried to measure the effect for a general rural population. You'd need a twin study or something like that to sort it all out, i.e. a bunch of twins where one grew up in the country, one in the city or 'burbs or whatever you're comparing it to.

If people in rural area have higher IQs (which I doubt) you'd expect to see a decrease as there's way less people living ruraly today than before.

Sometimes it's not how smart you are but if you can utilize that. Many people can't afford higher education, especially from rural areas, there's also stereotypes based on accents and mannerisms that could prevent growth at a company. People in rural areas are also farther away from large companies and may be unable/unwilling to move.