It’s rather technical but if you were considering getting smart home devices, you can use home assistant to replace the app on your phone. I followed this guide to make a very lazy Roku card for HA. Then, you can keep the TV on your LAN but ban it from the internet.

I have a pihole on the network to keep the ads off the TV but honestly I wish we hadn’t bought the thing. It sounds like you can’t use a different DNS? That’s a real shame. I’m more or less in your situation, seems like a waste to toss a working device just because it’s a rebellious piece of shit.