I'm not sure how the South Shore swung in 2020 though Trump certainly did win it but given that it's a suburban area with high levels of education that definitely went heavier for Trump then for Romney it almost seems to be an example of a national outlier and an outlier in the New York tristate area as well if you compare it to the wealthy suburban towns in Connecticut, New Jersey and Long Island that all swung heavily from Romney to Hillary and even moreso to Biden.
It swung 2 points to Biden:
2016: 73.5-24.0
2020: 73.2-25.8
