I have a 65" 4k LG Panel that has literally never been connected to the internet and never will be. It does not have nags nor does it automatically attempt to connect itself to the internet.
It works fine connected to an AppleTV 4k and and appleTV is the only smart TV software I'll use. It's smooth as butter, has no ads, and integrates with the rest of my devices with minimal setup.
I have basically the same setup. I like it, and agree its probably one of the best setups, but to be fair its still a user hostile battle field.
Apple has their dark pattern approach to promote the Apple TV+ service. Netflix refuses to participate in the global search. Apple constantly injecting ads about their content into other content.
When you say local files, do you mean files on a usb stick or hard drive plugged directly into the device?
I use Infuse on my Apple TV to access my videos on the network. It can pick up media from a samba share (or probably any other network share). There's more info on their site: https://firecore.com/infuse
It can also serve as a front end for a Plex server if you run that. While this isn't "local files", it works well and serves a similar purpose. Note: there is a very fair, cheap monthly/yearly/lifetime subscription required for any advanced features but it's free to try. I pay $12.99 for the yearly subscription and I'm incredibly satisfied. If this reads like an ad, it's not, I'm just really happy with it.
It works fine connected to an AppleTV 4k and and appleTV is the only smart TV software I'll use. It's smooth as butter, has no ads, and integrates with the rest of my devices with minimal setup.