The only reason to ask is if it's possible. The documentation says that it is not possible.I've given 2 good reasons why there is a need. One is that, if the OpenEVSE is only available as a 240V-connected device, it makes no sense for it to have a service level menu. It should simply be advertised as an L2 EVSE. The other is that if it has always been delivering 240V to the car when I was expecting and assuming 120V, I would have been seeing my POCO meter spinning forwards rather than being motionless due to being balanced by my solar array output.
It's trivial to end all debate. Simply take the cover off your OpenEVSE, plug it into the EV, then measure the voltage across the contacts on the contactor. Presuming that the input is 240V, the output will have to be 240V.
Sure we can talk about differential software that disables that menu when plugged into 240V. Or labeling that menu something else making it clear that it sets the maximum current based on the input voltage. But I severely doubt, like 100% doubt, that when set to L1 and plugged into a 240V input source that it delivers 120V to the car because it's incapable of doing so.