I can say it is safer to use outdoors with plenty of ventilation, but idk how it would affect the chickens, really. Unless they were on it a lot, or penned inside with this treated lumber, otherwise I would think it safe.

I think you're fine. The chickens aren't going to eat the wood.

problematic situation search in search engines like google that will could actually help

I have about a half acre of property, where I have pasture raised chickens. I share this property with another, who wants to use landscape timbers(that claim can make ground contact) to make retaining walls to keep property from eroding. I noticed the timbers looked green and did some research on what they could be treated with. It seems CCA has been phased out and it seems ACQ is in. However, I have found mixed reviews. Some sources says it's harmless and some say it's less harmful, all say studies back them up, but there are no citations to these studies. The only scholarly study I can find specifically states that it only studied acute toxicity and not carcinogenic/mutagenic effects and long term exposure. Is this stuff safe, will it leach out and taint the meat/eggs?