The fact that I am not an expert in the exact structures a hypothetical anarchist society could take doesn’t mean it’s impossible. Furthermore, as you allude to, their implementation in the real world would likely differ from any theoretical structure based on the experience and practical needs of the people involved. There are people building such organizations as we speak, and hopefully, as they gain experience, we can collectively learn which structures work and which ones do not.
In general I see anarchism as more of an aspirational process. The goals are to achieve human liberation to the maximum extent possible. Maybe it’s not possible to achieve complete global liberation (and I agree not to the extent that some individualist anarchists believe, i.e. the no rules people) but there’s good reason to believe it can be achieved to a much greater extent than current societies. I think that’s worth working towards, and even if we did achieve a more liberated society like Republican Spain, that process wouldn’t end there. We would keep iterating and tinkering to find the best and most free society we can reasonably attain.