What if being offline for a very long duration of time - means that when connecting it again - the firmware update bricks my TV?

We don’t see many updates that outright brick your product (yet). What we do see is updates that just happen to make your product run much slower than it used to. There’s always excuses why it is necessary, but in the end those updates tend to lead to sales of new devices.

Keeping the device fully offline is a defense against such an update.

Myself, I don’t see any reason for my TV to ever be online, so I take some comfort that it will not receive such an update.