we are due for another Carrington event and if it seriously screwed up 1860ish technology it will screw us over like no rogue nation can.
The threat is that a Carrington event induces what is effectively a high-power DC signal in transmission lines. It's worst for long ones, over 100km, with low impedance.
Back then data-transmission used copper wire and DC coupling to make a telegraph. The wires glowed erd-hot and shocked the operators and in places burned out. Today, long-distance datacomms is optical fibre. Telephone wires are rarely if ever long enough to get affected and I don't think a telephone offers a low-impedance path these days. Things have moved on since the days of bakelite boxes with electromechanical ringers.
The greater threat is to the power grid which is intended to carry 50 or 60 Hz AC. The power transformers through which it is coupled cannot cope with high power DC inputs and might burst into flames. Back in the 1950s we were terribly vulnerable(*) because the threat was not well known and there would have neen absolutely no advance warning.
Today, we have satellites watching the sun and so electricity utilities have an early-warning system. (about 15 minutes, but a lot better than nothing). Also the threat is understood and I hope that there are last-resort protection systems in place on the transformers connecting the long grid cables to monitor DC currents and internal temperature, that will disconnect from the grid if necessary to save the transformer.
So the result ought to be somewhere between a controlled shutdown of the national grids, and a cascading power failure caused by automatic protection systems triggering in an unplanned manner. A blackout is no fun, but it has happened several times (for other reasons such as carbonized squirrels) on the USA Eastern seaboard. Civilisation didn't collapse. A few hours to a day later when the event is over, they'll reconnect the grid to the power stations.
Move on a couple more decades, and the long-distance AC electricity grid will start to go the same way as the telegraph. It's more efficient to transmit power as high-voltage DC, and the technology of AC-DC-AC conversion is rapidly falling in cost. What was once impossible, then too expensive to use except on submarine grid links, will soon become the norm for any long-distance grid link. With a DC link, a Carrington event would just either add or subtract a small amount of energy compared to what is being transmitted. There would then no longer be a need to create a short-term blackout to save civilisation.
(*) I'd speculate, not actually on the edge of losing 20th century civilisation. The big transformers would have different times to catastrophic failure. As soon as the first one or two exploded all hell would have broken loose with the AC power they were transmitting, and ordinary AC overload protection systems would have cut in creating a cascade failure blackout but saving enough of the grid for life to go on fairly normally th next day. I'm glad it was never put to the test, though!