You can absolutely take cuttings from a plant in flower. It just takes longer for them to revert back to veg and start producing new shoots. You can even take a cutting off a flowering plant that's actually a bud, and even though itll take an extra 3-4 days to root, once it does, itll actually freak you out the way it grows n reverts back to veg. Kinda like watching popcorn pop, lol. Youll end up with lots of ADULT fully mature milk leaf looking leaves, and then after a couple of weeks, itll start to grow offshoots and start looking like a regular plant....except for where the bud was initially, lol. The bud will always be there from then on out, itll just have branches n leaves growing out of it, lol.
-You can take a cutting from a plant at any stage of its life and turn it into a clone. Its just a matter of how much work your willing to put into a cutting to make it a plant. You'd be better off just starting over from seed, lol. But yes, if its in the early stages of flowering, or if your taking a cutting that has not budded out yet, then you can absolutely clone from that plant, and have it still be productive to do so
-K1.