New AT&T SIM card for iPhone 12 Pro?

Hi:

Just upgraded my 3 year old iPhone X to a iPhone 12 Pro. I transferred the SIM card from the iPhone X to the iPhone 12 Pro. Love the new phone, but have a question re the SIM card:

Do I need to go into the AT&T store to get a new SIM card?

The iPhone 12 Pro seems to work fine with the old SIM card from the iPhone X. But there is no info regarding cellular service in the icon:

And some folks seem to say that if one wants newest security features and 5G, one does indeed need a new SIM card. Dealing with AT&T always is a huge time sink, often with what appear to be randomly generated answers depending who one talks to, so I'm hoping someone knowledgeable on the Apple forums can give me true scoop :)

Thanks very much!

PS the new phone is indeed a iPhone 12 Pro, but the dropdown menu below does not give that as an option, so used the most recent iPhone they have available from the menu, the iPhone 11 Pro.