2 Corinthians 5:17: if anyone is in Christ, he is a new what?

Answer: Creation

If anyone is in Christ, he is a new creation (KJV 'creature'). The old has passed away; the new has come!

“Therefore if anyone is in Christ, he is a new creation. The old has passed away. Behold, the new has come!”— 2 Corinthians 5:17 (BSB)