Yeah, but you can do this in the background without blocking the whole page. In fact you have to go to extra lengths to make it “block” the whole page. Maybe it’s just some css that sets the cursor to the “loading” image, and then ignores mouse clicks for a while, giving the illusion of doing lots of work…
While it will technically work, the old tube tvs had a 4:3 resolution of 5xx x 3xx or so, depending on if they used PAL or NTSC. Modern TV Interfaces are typically designed for a screen resolution of 1200x800 and 16:10 or 16:9, which means the fonts will be unreadable and half of the screen is cut off.