Juan Soto won the NL Batting crown with a .351 BA, the youngest NL player ever to win the title:

The 21-year-old Soto surpassed Brooklyn’s Pete Reiser for the youngest ever to take a batting crown. Reiser was 22 when he ended the 1941 season hitting a league-leading .343.

Chron.com

DJ Lemahieu becomes the first player since the start of the twentieth century to win batting titles in both the AL and the NL:

The modern era begins in 1900 and Hall of Famer Ed Delahanty won the batting title in each league at that time. Delahanty won the 1899 NL batting title with the Philadelphia Phillies and 1902 AL batting title with the Washington Senators, but the 1899 batting title is disputed, hence LeMahieu being the first in the modern era.

CBSSports.com

LeMahieu went two for three on Sunday to finish with a .364 BA.

Update: In looking at the final league leaders, Soto won the average triple crown, also finishing first in OBP and slugging percentage.