A 12V battery is fully charged at 12.6V.
When being charged, the charging voltage must be higher than the battery voltage to allow current to flow to the battery and charge it.
The rate of charge is determined by the current delivered by the device charging the battery, not by the voltage difference.
When you quiz the car and it indicates a battery voltage level greater than 12.6V this is because as a side effect of quizzing the car using the app it also brings in the DC-DC converter and charges the battery, shoving up to 50Amps into it depending on its state of charge.
To measure your battery voltage level correctly to need to put a voltage meter across the battery terminals when the car is completely powered down.
12.6V = fully charged
12.4V = 75%
12.2V = 50%
12.0V = 25%
With an ICE, 12V probably means you would not be able to start the car.
With a BEV 12V probably means you can't bring in the HV battery contactors and the car is then "bricked".
When the car is fully powered up and in the READY state the voltage measured across the battery terminals will be much higher than the 12.6V, typically anything from 13.0V to 14.5V.
It should be noted that it is understood that the BMS also looks after the 12V Battery Level when the car is powered off and the doors are locked. This is NOT true if you are using the V2L feature with the car powered off and the doors locked.