Tim Hardwick, MacRumors:

In iOS 14.5 and later, Apple has added a Waze-like feature to its native Maps app that lets you report accidents, hazards, and speed checks along your route when getting directions. Keep reading to learn how it works.

Given that, for me, the vast majority of the time this comes up I am behind the wheel, the simplest (and safest) way to do this is:

“Hey ‌Siri‌, there’s an [accident/hazard/speed check]” and ‌‌Siri‌‌ will send in a report to ‌Apple Maps.

Note that, at least for the moment, this feature is US and China only.