I tried that on my LG tv. The result was a 60 second timeout before I could use the tv when turning it on.
I ended up figuring out how to factory reset it and then never set up the wifi. No firmware update, but I don’t care since I only want a dumb monitor.
My advice: connect it to a restricted network, where it can successfully ping home and assert internet connectivity, but everything else (except maybe updates or whatever you want to allow) just fails.
A better, more useful approach is to have a DNS server on the home network (something like a pi hole), where all analytics go nowhere, Youtube isn't capable of downloading ads, etc., but you can still use the smart TV features you want. IIRC some TVs have internal DNS servers and only use those, so an ARP spoofing may be also needed.
fwiw you can often update the firmware via USB anyway—not sure about LG specifically but Samsung TVs support this. It's often worth updating the firmware as, like a lot of software these days, it sometimes ships half-broken.
