You do, however, typically need to set “low power standby” or whatever in the options somewhere - it’s usually not enabled by default - the default is usually to turn the screen off but leave everything else running. Mine drew about 5W in “normal” standby, and is immeasurably low (from our household inverters - I live off grid) in low power standby. It takes about 10 seconds to boot - no big deal.
I believe the low power mode is required (by UK law, at least) to be enabled by default. It's pointless otherwise as almost nobody will go and enable that mode.
That is going to vary a lot depending on the TV. I suspect a lot of modern "smart" TVs consume a measurable amount when idle.