Not really. Many other countries also have a left-wing/right wing split in their politics. There is a lot of sharing of thought and cross-influence between right-wing politics and left-wing politics in different countries. Figures on the British right like Lord Monckton [1] or Nigel Farage [2] find many admirers in American and Australian conservatism. Conservative American journalists write puff pieces extolling the virtues of Marion Maréchal [3].
And I think you will similarly find a lot of exchange of ideas and thinkers on the political left between different countries too.
[1] https://www.heartland.org/about-us/who-we-are/lord-christoph...
[2] https://ukipwsx.org/nigel-farages-speech-at-us-heritage-foun...
[3] https://www.theamericanconservative.com/dreher/marion-marech...
After Biden wins, I'd guess we'll have a couple years of laxer enforcement and that will doom the alternatives.
If social media companies will be bifurcated as you say, it’ll be a tiny fraction of their American audiences - leaving the rest of the world sticking with the mainstream. Those smaller Ameri-centric sites will fail to reach critical-mass needed to sustain themselves in the long-term and hopefully those movements will fade into the background.
Your comparisons to the *chan imageboard splintering is apt, but look at how the more extreme chan sites have been having in finding a web-host (with enough capacity) to host them.