Basically, the only way is to disconnect the TV and use it as a dumb screen. Lineageos supports a few set top boxes (see here).
I heard (take it as hearsay) that some smart TV periodically capture screenshots of what’s on screen and upload it, so it actually disconnecting the tv from the network could (again, hearsay) make a real difference.
I must say, this is really creepy.
In your shoes, I’d put some effort into explaining what (legitimate) use case you have, least people won’t be much inclined to help.