Yes-ish
it depends…
let me explain, I have a 3 bike stable, and depending on where and when I’m riding will determine if a helmet is needed…
Bike one; an old rigid steel Fila Taos MTB converted to a roadgoing singlespeed, slicks instead of knobbies, and a Surly Singleator chain tensioner, this bike is ridden around town (Dover, NH) at work, when I go out to lunch, I typically hop on the bike, it’s about a mile or so round-trip to the furthest away place, top speed is around 15 MPH, average is 8… this bike I don’t wear a helmet on
Bike two; a Trek 4500 MTB, currently with slicks, one of my road-going bikes, for my easier recreational rides, on the back roads around the house, sometimes I swap out the slicks for knobbies and do some light offroading, top speed is around 20 MPH on road, average is 8, this bike I sometimes wear a helmet on, but it’s not mandatory
Bike three; a Giant FCR-3 flat-bar road bike with Shimano SPD flip-flop pedals (SPD cleats on one side, platforms on the other), this bike is my highest-performance bike, top speed is 28-30 MPH, average is 10-12 (on the pedal flats), and I’m typically on it for 5+ miles on average, this one I DO wear a helmet on, as I’m moving pretty quickly for a “Clydestale”…
the Giant sees the most road time, the Trek sees the least (I’m trying to get one of my work neighbors to buy it off me)

Given also that my
(No spandex!)