Maybe. I'm not sure if FPTP necessarily leads to authoritarianism, but there's a whole bunch of countries that sill use the system

https://en.wikipedia.org/wiki/First-past-the-post_voting#Cou...

I think, though, that the US won't go full top-down authoritarian, because a large enough portion of the population is armed. Should some kind of coup ever be attempted, it could well spark a civil war – which is still doom, but not a subjugating kind of doom.

The population is unarmed. Small arms don't count, they're good for the shooting range and mass shootings, but not against a modern military.

But yes let's hope there will be elections again

Numbers matter. Only a small amount of insurgents are needed to occupy the military, but if even 2% of the civilian population took up arms, the situation would become untenable. All the armed forces together constitute not much more than one million troops. And there would be also conscientious resistance within the armed forces to executive orders to shoot civilians.