Yes, you can turn on an electric car while it is charging, however, you won’t be able to drive it away. Electric vehicles will not let you open the charging socket unless the car engine is off, although you can still power it on for other things such as using the heater, entertainment systems, apps etc., while the charger is plugged in.
The main reason potential EV owners ask this question is the fear of having to sit on a cold day with no heaters running in an electric car, freezing away while waiting on the car charging. This shouldn’t be a concern though, as you can turn them on just the same while you sit and wait.
The vehicle will lock the steering wheel and will not present the drive option as a safety precaution when a charging cable is connected. This is simply to prevent you from driving away while the EV charging cable is connected, damaging the cable, the charging station and potentially the car socket.
You might think there’s no reason to want to drive while a charging cable is connected anyway, however, someone might feel like they want to reposition their motor slightly in a parking space while it charges, in which case you would have to disconnect the charger from the car and move it.
There may be slight differences from model-to-model in terms of the drive/ start mode options, though every EV on the road currently and in the foreseeable future will allow you to turn on, but not drive the electric car while charging.
Some manufacturers also have some safety guidelines and recommendations for sitting in an EV while it charges that you should check out before doing so, especially for people with pacemakers and other electrical implants.