>Request for source on illegality [...] I don't see where it says anyone is refuting that

the regulators are the ones refuting google's claims. the headline opens with: "Finland's regulator says the environmental review came too late"

and the second paragraph of the linked article says:

"Google was apparently so eager to build its new data center infrastructure in Finland that it began bulldozing large swaths of forest __before the required environmental review of the full plan was complete__."

typically, doing something before the environmental review gives you a notice to proceed is illegal.