His increases were mainly in South Florida where Cubans abound and the message was simple - Biden is a communist is enough to win their votes.
The other area was south Texas border. Biden has very little appeal to Latin Voters but Biden appealed better to white voters. The Republicans were better at messaging to the Latinos in this election.
The irony being the Latinos strongly identify with social and religious values of the Republicans (yet not with Biden who is a catholic like the majority of Latinos)