Ensure any "smart" device like a smart TV is not connected to the internet nor your home wifi. Do not accept any TOS/EULA on a smart TV and do not use any built-in "apps". Use them only as dumb monitors with hardwired HDMI inputs.

Obviously avoid any of the myriad of smart devices there are out there now, like pretty much any robotic vacuums (they literally have spycams on them now), Amazon Echo, etc. I assume you already know better...

Do your research on any car you might purchase. Cars are trending towards being smartphones with wheels. Anything that might have a feature like remote start is often now using cell service tech not limited range/offline radios, and usually that also comes with a bunch of ET Phone home nonsense as well.