No, the outright political warfare in the US you are alluding to began much earlier than 2020. Things were getting quite ulhealthy already back in 2015/2016, probably even earlier. The "black swan" for this deep division was (I believe) not the epidemic, but the proliferation of the smartphone and social media, and the earlier transitioning of traditional news to infotainment format.

I'd attribute it to 2008 financial collapse, and in general, the pressure put on the middle class that began a decade earlier.

And I genuinely believe blaming things on social media and news is just a diversion so we wouldn't look at the main issue.