Seems to be referring to this part of the text:
> Observation
> Chrome is deprecating the blocking capabilities of the webRequest API in Manifest V3, not the entire webRequest API (though blocking will still be available to enterprise deployments). Extensions with appropriate permissions can still observe network requests using the webRequest API. The webRequest API's ability to observe requests is foundational for extensions that modify their behavior based on the patterns they observe at runtime.
No idea if that's the API that adblockers use (or just a part of it)...