that depends on local laws. depending on where you live, it may be illegal to ride high speed ebikes in the first place.
Beyond a certain speed, full-face helmets become a practical matter rather than merely a safety or legal matter. Can't hear with the wind rushing in your ears, can't see with the wind in your eyes.
> Can't hear with the wind rushing in your ears.
Some cyclists use a product called Cat-Ears. It's just some synthetic fur that attaches to the helmet straps akin to having some sick sideburns. It works great.