By chance I came across the below info when browsing another topic: XIAO BLE Sense in deep sleep mode.
cut-n-paste
"Better to use the 3V3 pin for lowest power consumption.
Seems like powering through the battery adds ~2uA (guessing quiescent from the 3V3 LDO, no part number given in schematics).
Powering through the USB-C port adds an additional 750uA, due to the active supply current of the BQ25100 Lipo Battery Charger IC.
"