I haven't seen that many (elderly) people in The Netherlands on e-bikes that used a helmet this year. The only people that wear helmets are the ones that have a speed padelec/mountainbiker or racing bikes.
I guess it really makes a difference if you're cycling in the Randstad, or one of the other greater cities, or outside of them. I'd say about 50% of elderly people I see on e-bikes (and I cycle about 4000km / year, almost all outside of bigger cities) are now wearing helmets.