PSA: If it's a recent-ish LG TV, you can root it and install an ad-free youtube app in just a few clicks. That said, one might be afraid of potential future breakage/maintenance burden from installing homebrew software for a relative.
Apart from SponsorBlock in YT, the most useful thing I've found is the Hyperion sender app. I'm really looking forward to building my DIY Ambilight when the pieces arrive, and it's really nice to automatically capture all output, instead of capturing through HDMI.
Not that I'd want it actively connecting to the Internet either way, but if I could run something more stripped-down than an OEM stock image it would... almost make a smart TV attractive?