If a Data Saver user is on a 2G-speed or slower network according to the NetInfo API, Chrome disables scripts and sends an intervention header on every resource request. Users are shown a Lite Mode UI in the omnibox. Users can enable scripts on the page by tapping “Show original” in the omnibox UI. An intervention report is sent when this optimization occurs.
Docs: https://wicg.github.io/netinfo/#dfn-effective-connection-types https://developers.google.com/web/updates/2018/09/reportingapi https://www.w3.org/TR/reporting/#intervention-report