I know its a late reply but i just search this today and this was the first site that appeared so i will reply for future users. duplicate on Affinity Designer is ctrl + J but it works better than illustrator if you have an object1 and use alt to duplicate you create object 2 if you keep alt pressed and you rotate the object2 if you press ctrl + J it will repeat that rotation and if you keep ctrl + J you will create a flower.
where i learn this from(it has a video):
https://webdesign.tutsplus.com/articles/how-to-power-duplicate-in-affinity-designer--cms-25010
