Contrails are water vapor

Cloud seeding is something different and usually involves injecting small particulates for water droplets to nucleate on.

Where chemtrails are usually a reference to a particular chemical introduced to disperse into the air (not nucleate with). Often as part of a conspiracy saying all aircraft are taking part in blanketing the skies with whatever chemical agent is the flavor of the week. I’ve heard people say it’s mixed into the fuels, etc.

However, there are very rare instances where a plane (excluding crop dusters) will actually release chemicals via fuel into the air. When a plane has to make an emergency landing (especially right after takeoff) they may actually dump fuel in order to reduce weight and to minimize the explosive/fire hazard from the fuel.

Here’s a video by Captain Joe which covers contrails and fuel dumping

https://youtube.com/watch?v=e20vaAtncsM&si=78R8Qy0tg3AcB7e8

....that didn't take long....

Chemtrails are not real.

while cloud seeding is a thing, this is not what the conspiracy theorists are pointing at as 'chemtrails'. you can know that because cloud seeding kind of requires clouds to function. which, would obscure any smoke trails left by the silver iodide. cloud seeding takes already-condensed-out water vapor (aka, clouds,) and gives it something to attach to in large enough quantities that the droplets fall out of suspension- that is to say, they, uh, precipitate... and... uh... become precipitation... (aka, rain. or hail.)

this is done for a variety of purposes. the first is to cause clouds to precipitate in specific areas (I.E. LA does this over the San Bernardino Valley, to cause the precipitation to help with their hydro electric plants. And California does it up in the mountains to generate snow pack.)

Then there's the opposite- for example, around airports, they'll seed fog banks to get rid of the fog. or, in a bit more of a vane example, they seeded clouds to prevent it from raining on the Beijing Olympic's opening ceremony.

Meds, now!

You are technically correct but only if you are loose with how you define chemtrails.