Most data centers would normally be protected by FM200 which is waterless. It’s cost effective and won’t damage your IT investments compared to water-based agents.
We still use Halon. And I read this statement: Because of the Montreal Protocol, ozone-depleting substances, such as Halon 1301, are no longer used in new fire suppression systems. Governments around the world have already mandated the decommissioning of Halon 1301 systems.
I am not sure if the US govt has mandated it yet or not.