The Access-Control-Request-Method request header is used when issuing a preflight request to let the server know which HTTP method will be used when the actual request is made. This header is necessary as the preflight request is always an OPTIONS and doesn't use the same method as the actual request.
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.