when changing tree generation in the config I don't notice a difference, even when I change it to zero trees still spawn. This maybe a bug ore intentional but the option of disabling archtrees maybe useful for modpack developers in the future.

This is now fixed here, and the config has a new name. https://www.curseforge.com/minecraft/mc-mods/ars-nouveau/files/3647553

I have the same issue :<
It's not that 0.0 specifically doesn't work either
I tried setting it to something like 10^-20 and it also made no difference