Sometimes you have to be a bit more pragmatic. I’m not aware of any TV with HDR, Dolby Vision, OLED, etc. that isn’t smart and reasonably priced. Your best bet is to buy a smart TV and block Internet access.
Another thing you can do is visit the selfhosted subs and they can help you out with other things like pihole for blocking ads and intrusive network activity on your home network.
That was my first NAS OS, too! It’s a gateway drug 😆