However, the law does often distinguish between modulating/pulsating lights and flashing ones. In the US, federal code 49 CFR Part 571.108 S7.9.4.1 explicitly allows modulating headlights on motorcycles[1]. From time to time I do see motorcycles whose headlights pulse. I hate it - it makes them easier to see but harder to gauge distance, and harder to focus on all the other traffic and pedestrians on and around the road.
[1] https://www.gl1800riders.com/attachments/federal-law-motorcy...