It's the adjectival form of the word "affect" in its noun sense, meaning "mood" or "feeling". This form is pronounced differently: A-fect (emphasis on the first syllable, with the vowel like in "rat").
"Affective polarization" is "people being polarized in how they feel about each other", i.e. animosity towards people in the other party. It's a technical term used by sociologists and not in common use, but it's not a typo.
Additionally,
“ We see indications of empirical validation in recent events. Prior to 2019, one might have assumed that a global pandemic would bring together those who disagreed on issues for which hot-button righteous indignation was a luxury that could no longer be afforded. Instead, mask wearing became a partisan crest that identified friend and foe on a partisan battlefield. Similar dynamics can be observed in the two impeachment trials of former President Donald Trump. In the first trial, evidence of collusion with a foreign government failed to exert the expected unifying effect. In the second case, an attack on the US Capitol initially elicited bipartisan outrage, followed by a reversal of position among Republican leaders in the weeks leading up to the Senate trial.”
"Nevertheless, we make no claims about the model’s predictive accuracy. The model is highly abstract and remains to be empirically calibrated and tested. Nor can we assume that tipping points would obtain in radically different applications, such as affective polarization, voter polarization, or media polarization."