If you have nay knowledge of networking (or want to learn), start setting up restricted VLANs to isolate your smart devices. Only allow them access to specific services/devices like your media server.

For dedicated hardware, there are plenarily of options. A Raspberry Pi will work to start with, there are Linux images with Kodi such as LibreELEC and osmc (I have used both in the past and they worked fine), and Android TV images also that can run apps. I suppose you could also set up a generic Linux install and run the Jellyfin client or similar - not sure if there any turnkey options for that.

We have a couple of Apple TV boxes and they perform well, the Jellyfin apps for them have really improved in the last year or so too.

LG have been caught using the Internet connection of connected devices (like windows computers) to snoop on your network.

Do you have any sources for that? Not doubting it just curious about how that works.

Unfortunately that will probably also void any warranty. Better to restrict access at the network level.

It shouldn’t be necessary or expected to perform surgical interventions on devices to make them respect privacy.

I didn’t know LG webOS rooting was a thing, that’s interesting to know.

There is an open source version of webOS, although I don’t know how it compares to the stock LG version. Maybe there will eventually be something like a LineageOS equivalent.