Is "OFF" Really "OFF"?

Unplug it AND take out the battery. Alternately you could also keep it disconnected from the outside wired world and in a robust faraday cage.

Of course the value is in the connections. No one is going to be interested enough in your solitaire prowess to spy on your computer if it isn't researching or disseminating information to other places.

On a modern computer you can assume that "OFF" is not really "OFF". The main processor is probably not crunching numbers, but the USB ports are looking for keyboard (possibly other also) activity. The LAN circuits are probably looking for whatever outside activity can initiate a "Wake On LAN". Thus, to some extent, they are designed to let the outside world get in. Setting up security is very helpful, but you are not paranoid to worry that someone can get in, have their way, and leave. If they wish to, they can destroy the computer on their way out. If they wish to, they can leave with the computer looking like they were never there.

An old fashion power strip with a mechanical power switch will keep a desktop or rack mount computer "OFF". Laptops are a bit more of a problem.

You are correct that there is often "parasitic" power that stays turned on even when you think it is off. That's why my TV is unplugged--I haven't watched it in almost 6 years!

I turn my computer off every night. First I shut it down the "official" way, then switch off the power strip so that no power is going into the computer or other peripherals. But you might want to leave the clock battery installed; it's difficult to get to anyway!

I think laptops have a power-off switch too--at least my ancient one does.

I've had many laptops over something like 35 years. They were mostly Macs, plus a couple of Dells. AFAIK, none of them ever had a true power-off switch. Most, if not all, of them had a power button, but that is a momentary contact device which "tells" other circuitry to shut the power off to most of the computer, if not all of it.

As you hinted, the Real-Time-Clock continues running. I once serviced a 20-year-old desktop Mac that still had its original soldered-in PRAM battery (which also powers the RTC), and hadn't been used for several years. As I recall, the time was off by a couple of hours, but the date was still correct.

I know of only one way people will stop listening; become uninteresting, boring, and harmless. I have stopped listening.

The camera and sound is probably still on… for,… you know… future use.

A1) presenting it to the inlet of a shredding machine usually works just fine:

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A2) -

A3) -

A4) see A1 ↑.

The best thing to do is move forward. Being forgetful might help. It does on government level. I mean seriously