Beetle ESP32-C6: mV from PIN 0 changes on USB charging. Any way to isolate actual battery mV?

Hello forum members.

The board in question is a Beetle ESP32-C6.
 

I am displaying the mV from PIN 0 (int currentBatteryStatus = analogReadMilliVolts(0) * 2;) on an OLED during testing, before showing a charge percentage.
There is a notable difference in mV output on PIN 0 between discharging and charging via the USB-C port. I was expecting the mV from PIN 0 to increment as the battery stores more charge, and then stall at the battery's max charge, but it suddenly jumps beyond the max charge when the USB is plugged in. Is that expected behavior?

I want to be able to indicate on the OLED when the battery is charging, and fully charged. Relying on the onboard LED is restrictive, especially inside a housing. It looks like the charging chip is not exposed for taking a charging / not charging state.

At a random state of discharge, I took these readings:

Battery not charging:
OLED display = 3734

multimeter = 3.88V

Battery is charging (USB-C):

OLED display = 4160
multimeter = 4.10

charging LED is on.
 

I expect some discrepancy between the Beetle and meter, since the meter is a cheap one.
At one point the plugged in mV was over 4300.

Thank you.