Does my iPhone XR support LTE?

My iPhone XR keeps telling me that it may not be operational after 3G closure but I understand that it has VOLTE available and assume that it's automatic as I don't get any options to change the setting under "Mobile Data Options". Can someone knowledgeable please confirm whether that's the case and I'll work out how to avoid listening to the message every time I dial out...

[Re-Titled by Moderator]