1. Many anarchist movements do not demand this much change. They only demand removal of specific forms of hierarchies they think most problematic. The Occupy movement for instance was demanding the curtailment of the political power of the 1% over the 99%. Its always better to think of political movements as directions of evolution in political space, rather than specific destinations.
2. Then how do anarchists propose that laws/constitutions be imposed? By consensus and discussion. By making sure everyone is on board. Or by temporarily giving someone conflict resolving power (as in the Debian case). Plenty of societies and organizations operate this way, and work fine. Read The Dawn of Everything for some historical examples. See a region in Syria [1] as a modern example.
[1] https://en.wikipedia.org/wiki/Autonomous_Administration_of_N...
Then it mislead you. Anarchist organisations aren't typically characterised by large, long and complex sets of policies, constantly evolving, that are strongly policed. Often by bots.
This is the reaction from one software engineer that stumbled into Debian infrastructure: https://lists.debian.org/debian-devel/2023/09/msg00334.html
To quote one part of that email:
I've been maintaining free software for 30 years so I've got a lot of experience with a lot of different tools, and I've rarely encountered anything that is as comprehensive and well-documented as all this stuff is.
And while it's a flat(ish) style hierarchy, it has leaders (the DPL), a judiciary (the technical committee) and even behaviour police (whoever polices the conduct - it is policed).