Can airplane mode be maintained during a system update?
If you want to block communication with your mobile network provider there is a second option: You just have to make sure the MNO can not identify your devices.

You can easily achieve that by removing the SIM card from your device.

This does not work of course in case you have a phone with eSIM and you use the eSIM (as the eSIM can't be removed physically from your device).