Can we update ios 14.6 by mobile data

Only if you have an iPhone 12 on a 5G network. Otherwise it is by WiFi or through your computer.

Sorry no.

Wifi network connection with Internet access is mandatory to update your iPhone wirelessly (no cellular data, no personal hotspot, no VPN connection are adnmitted).

You can update it using iTunes on a computer, but the computer must have Internet access.

Regards

Giulio