I don’t have a use case, so I can’t test. This looks promising, though:

Shared Progress Across Copies: Progress is now stored against the Calibre book rather than the file checksum, so different copies/formats of the same book on different devices stay in sync. (PR #1225)

Just encase your TV room in lead so it can’t get a signal out. Ezpz.

In seriousness completely eliminating the possibility of surveillance is impossible, but that doesn’t mean you shouldn’t make it as hard as you’re willing to give up convenience for.