Well, let me tell you. Rather than mess with Google I marched myself downstairs, grabbed a magnet off the refrigerator and in my house shoes and short sleeved shirt braved the 5°F elements to prove a magnet won't stick to my very lightweight tailgate.
It stuck.
I moved it to another spot.
It stuck again.
I'm pretty sure that at some point I read marketing material that claimed the Ram HD (at least in 2023) had an aluminum hood and tailgate. But since that is clearly not correct there's no point in trying to track that down.