Blätter gelb in 3. Blütewoche

That can happen during the flowering stretch, yes. It's a nitrogen deficiency, but no problem. The plant has cannibalized itself, as mentioned, to keep the upper parts healthy. I wouldn't worry about it, just trim the leaves if they die off. There's not much you can do since your plant mainly needs phosphorus and potassium in the next few days, so there's no point in feeding it again now. Just enjoy that the rest is healthy, the leaves are unnecessary anyway👌 Have a relaxed weekend, feel free to message me privately if you want. Bottom right👍

It doesn't really look like a proper deficiency, more like a natural progression. Do you generally feed the lady? BTW: looks great! Keep it up!

Hello xhibo, Yes this is clearly a Nitrogen (N) deficiency. You need to add just a little Nitrogen into your nutrient solution. 25% from the adviced amount will be enough because the plant is not using it that much anymore like she did during the vegging phase. Next to that your plant does look great buddy! Happy Growing! 💚

I don't think it's a deficiency; otherwise, the symptoms would be visible all over the plant. I believe it's a natural process where the plant sheds its less useful leaves.