Google is telling me that the mesh for a Faraday cage that would block WiFi could have hole sizes up to about 5 mm. Suppose you made your faraday cage (or at least the part that goes in front of the screen) out of 40 gauge wire (0.07874 mm diameter) with the wires spaced 2.25 mm apart.

On a 70" 4K TV a pixel is about 0.4 mm x 0.4 mm. If the mesh were close to the screen I think about 30% of the pixels would have wire in front of them. Of those 30%, 1/6 would both a horizontal and a vertical wire in front (let's not go crazy and talk about orienting the mesh diagonally or anything like that), and 5/6 would only have one wire in front of them. So that's 70% of pixels not interfered with, 25% having one wire in front of them, and 5% having two wires.

The 25% with one wire crossing would have about 20% of the pixel occluded by the wire. The 5% with two wires crossing them would have about 36% occluded.

My guess is that the screen could be seen pretty well through that.

Make life easy, just stop RF getting to and from your TV by cutting the WiFi, Bluetooth and mobile antenna leads.

Simple, go wired and encase the house in a faraday cage.

Really, anyone who's lived in a sufficiently old house knows you can run your own Wi-Fi in a Faraday cage. Just probably not between rooms.

Underfloor foil insulation works pretty well as a cage. It also adds a nice electrocution risk when installing and is banned in my area for this reason.

Metal lath under the plaster. Ripping that out was a mess.

Houses finished with stucco tend to do this as a side effect, since stucco is applied onto a fine metal grid screwed to framing.