With California's release of its supplement to the 2020 General Election statement of vote, here's all of the cities that saw a double-digit swing towards Trump last year.
https://www.sos.ca.gov/elections/prior-elections/statewide-election-results/general-election-november-3-2020/statement-vote

And on the flip side, the areas that saw a double-digit swing towards Biden from 2016 to 2020.

California's top Biden cities/top Trump cities in the 2020 general election.