LG (at least for my OLED model) supports firmware updates over USB, and posts firmware updates to their website. It's a very smooth flow -- my years-old TV has never had an internet connection and is up-to-date.
Thank you, and babypuncher, for this advice! I avoid using the tvos but dislike how a parade of web connected ads pop up if I hit the dashboard button by accident. Glad I can airgap it again.