What's your question? Ask

It sounds like a problem with nutrient ratios. Too much nitrogen and not enough phosphorus and potassium can cause these symptoms. In general, the soil could be too rich in nutrients. These flowers cannot handle fertile soils.

Test your soil for deficiencies, overloads, or pH swings and correct as needed. Here are some articles that will help:

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm

This article will help you to grow the flowers:

https://www.gardeningknowhow.com/ornamental/flowers/cosmos/growing-cosmos.htm

There are quite a few plants that have this growth pattern. Unfortunately, the scent of the plant will be the best way to distinguish what it is. That, or waiting for some type of flower structure.

My top guesses would be, either, Cosmos bipinnatus or any of the Artemesias.

If the blooms are still pretty and colorful, that means that the seeds will not be mature. It will be necessary to pick from a flower that has already died and dried. Unfortunately, picking blooms early, you may find that most of the seeds are not viable.

Make sure to allow the flower to die, almost, completely before picking for seeds. This article will help:

https://www.gardeningknowhow.com/ornamental/flowers/cosmos/collecting-cosmos-seeds.htm