When 5G is rolled out completely will iPhone 11 Pro become useless?

Of course, not!!! Nor will any other cell phone that can communicate via 3G, 4G or LTE.

With the advent of 5G, carriers around the world are decommissioning their 2G networks, which were put into service about 30 years ago. US carriers will likely decommission their 2.5G networks, put into service about 15 years ago, a bit later, since the installed 2.5G customer base will prove more difficult to dislodge. The two reasons for decommissioning are repurposing the bandwidth and repopulating the transceiver shelves in the cell towers.

We last saw this in 2004, when networks started decommissioning 1G (analog) networks in order to implement 2.5G. And we will see it again in a decade or so, when 2.5G and 3G need to make way for 6G. Until that time comes, I wouldn't worry.

The "5G" standard hasn't even been finalized yet! The "TV host" who said that is basically an idiot.

Of course not.

Yes.

It will take many years to roll out 5G and some parts of the country (like mine) will not see it for 20 years.

Turn off your TV until 5G comes out in your area.

There will probably be 10 new iPhones sold by the time 5g is initiated?

No, when 5G rolls out (which will still be in about 1/2 a decade) your phone will still have 4G/LTE data and calls will still work