Clone

If you know that the plant is feminized you don't have to wait until it shows her sex, when i top my plants in week 3 i usually already use these as clone, and they root perfectly without any issues.

I agree with Thinlizy. I read in a book that taking cuttings from a plant should be after 49 days of life. You can do it a little sooner but if you take it too soon the cuttings may not be strong enough to pull through and start making roots again. I mean a plant three weeks old is just beginning her veg stage. Plus I would wait to see what sex it shows. I doubt at three weeks she’s showing herself or himself. Anyway good luck friend you’re in for a bit of a learning curve. 🤙

I take my clones around week 6 of veg. Depending on the plants you could take them a little earlier. I also take them a week before i flip my plants into flower.