Thanks for the question.

You could certainly remove the flower heads now, let them dry, and harvest the seeds. If your delay things too long, squirrels and birds will discover them.  Wrap them in a zip-loc bag, place in the refrigerator, and use them in spring 2022. However I fear that you may be disappointed in subsequent reseedings, however admirable they might be. Your sunflowers are most likely hybrid plants. This would be especially true if they are tall (over six feet). Sunflowers generally are self-pollenating. So the seeds that you will be harvesting would represent offspring from hybrid parents. These offspring will be all over the place with respect to their sizes, flower appearances, and flower color. I speak of this from my own experiences. You would be better advised just to buy new seeds in 2022.

Please get back to us with any additional questions.