I had to take it to a dealer to get the function activated. If you hold the + button on your display (if you have the purion like me) and no light symbol appears on the display then it needs dealer activation. Some bikes may come with it already activated whether they have lights fitted or not, mine didn’t.
On my other shimano motored ebike, I was able to do it with an app on my phone (but not the official shimano app as they took that function away, **** muppets).
The amount of battery reserved for light function can also be set, on the bosch I got the dealer to set it for 6wh, and on the shimano I set it to 20mins (different metrics for different manufacturers) but I certainly don’t need lots of extra battery being reserved for light function.