do you have the option to switch keyboards when you are in a screen that allows typing?
the first image i posted , if you look at the bottom right of the phone, you see a keyboard icon. you tap that and it brings up your other installed keyboards (if any).
what version of the samsung keyboard do you have?
if you know someone else who has a note 8 (or maybe s8) on att, ask them if they have the keyboard.
you can also call a local att store and ask if they have an oreo updated note 8 on display and see what version they have and if they can pull up the gifs.
you can try to clear the phone's cache (instructions are all over the internet).
if no success on any of that, you may have other issues that may need updated support, since it was easy to set up, as i have shown.
you can also contact samsung.