Often you must connect it to download updates and set it up. For my last TV I even had to make a Samsung account for god knows why just to set it up. After that I think you can disconnect from WiFi and use it just fine. You can also turn off the system UI if you have an Apple TV or similar so that it goes straight into Apple TV rather than showing the pre-installed apps.
My Samsung Frame TV has never been connected to the internet (and never will be), but still shows constant nag messages. Not only do I have to not fall prey to them, but also must hope that anyone else using the TV does not lest I get ads foisted upon me. I will never buy another Samsung consumer product under any circumstances.
I've got a samsung tv that asks to set up an account, but I can still apply firmware updates with a USB stick, and the TV works fine if you ignore the prompts, and you pretty much don't see the prompts if you use a 3rd party remote that asks for specific inputs.
