Long term motorcyclist here. As a FWIW, there are studies showing that the majority of motorcycle fatalaties are at/under 35MPH. Electric bicycles are capable of 20+ so they're exposed to a similar risk. At least get a bicycle helmet and use it. Also maybe gloves; even at a standstill a fall-over can mess up your hands. If you rent electric bikes consider a lightweight daypack to put your helmet in so you've got it when you need it.
Back in the 60s when I rirst started riding - and my state didn't have helmet laws - I tried to stabilize a fellow rider (helmet less) until the ambulance got there. When they got to us they told me he was 'already gone'. No visible injuries, so probably a concussion; I never found out. Come forwards to the 90s and I lost a close friend to riding a bicycle w/o helmet, and that was *definitely* a concussion. He lived for about 3 days, never woke up. His mom was a widow and he was an only child. :-(
The only silver lining: he was super healthy and an organ donor; the recipients might still be alive.