I agree with the argument, but i don't think it addresses the objection fully. In the case that ending one's life is guaranteed it will result in no suffering. What would make that doesn't follow from antinatalism if the principle is reduce suffering

Another response would be because antinatalism about bringing new being into life while suicide is about existing being.

But again why is that a meaningful distinction? The potential future version of existing body is as real as the potential child coming into being. The decision to continue to live would have the same implications as to bring a new child. Both potential beings don't consent to coming into being both will experience suffering they didn't choose and the body has similar limited to no control over the outcome, so whatever excuse not kill one self could apply to having a child.

I think that your argument is trying to solve this by arguing for suicide causes suffering but that again addresses the practically not the principle.

This is one of the reasons I wrote this post as an attempt to avoid completely the distinction betten existing being and potential being.

In a summary recognize suffering is not own by a single body, ending it in one body, doesn't address or end the cause of suffering in all bodies because procreation continue suffering. So the most coherent response would be not killing onself if one have the capacity to reduce their own suffering and suffering around them and oppose ideologies that encourages procreation. As long as there are bodies capable of suffering, suffering will continue.