When the population of Earth was 1.2 billion, probably more then 1 billion of them had practical real world experience in farming without electricity, electric water pumps, or chemical fertilizers. A similar number of people knew how to manage and care for horses, and had access to them.
Communication back then was based on an efficiently designed mail system that had evolved with centuries of experience. If you delivered mail, you understood horses and wagons well. In the alien's blackout, it would take years for some places to learn why the lights had gone out, and who, if anyone, was still president.
The roads would work for walking and bicycles, but canals would need electricity to open and close their gates, and to coordinate. And all of them would be clogged with beached and unpowerable ships, aka
Evergiven.
And of course within days, the cities would all be on fire from everyone lighting candles and trying to heat skyscrapers with improvised wood burning stoves. (Since the flashlights, emergency lighting and radios don't work, this is much worse than a blackout.)
And of course, everything above assumes that everyone is acting rationally to solve the problems and re-establish a new working economy. As opposed to Mad Max larping, which is what more people think they know how to do.
Humanity would survive, but the die off would be apocalyptic, with perhaps 100 million people left alive before things stabilize and the population begins to recover. That population would be quite unequally distributed, with the least developed cultures fairing best.
