Humans have been doing the whole sulfur dioxide thing for decades. In 2020 cargo ships began to use fuels with less sulfur in them to reduce sulfur dioxide output. The result, was a marked increase in sea surface temperatures because the aerosols used to help block some of the sunlight.

It's arguable to call it geoengineering as that implies purposeful engineering is ongoing. Whereas we were literally just burning sulfur rich fuels for cargo ships.

The reason people associate it with chemtrails is because sulfur dioxide is touted as a key component in the exhaust trails left behind by aircraft. While there may be trace amounts of the stuff in jet exhaust, this is not purposeful geoengineering as it's just a byproduct of fossil fuel use. A more visible one because it's easy to look up in the sky and see planes leaving trails compared to seeing the faint haze left behind by cargo ships in the middle of the ocean.

Cloud seeding is a thing in very small regional efforts for promoting cloud cover and even rainfall. And these are purposefully done to achieve those two outcomes. Usually they're done near dry places that have too much sun and not enough water. Despite some of these operations taking place, their effects are miniscule when compared to the scale of global operations that aren't trying to purposefully do any geoengineering.