Where can I find the blue LED associated with 14?
VBAT_ENABLE is associated with 14 (P0.14) and LED_BLUE is associated with 6 (P0.06). You need to refer to the following files and schematics.
C:\Users\username\AppData\Local\Arduino15\packages\Seeeduino\hardware\nrf52\1.1.9\variants\Seeed_XIAO_nRF 52840_Sense\variant.cpp and variant.h