The most controversial aspect of the extension manifest v3 is the upcoming changes to the webRequest API. In v3, Google has changed the API so that extensions can only monitor browser connections, but not modify any of the content before it's displayed.

Instead Google wants developers to use the declarativeNetRequest API, which has the browser, not the extension, strip content or resources from a visited web sites.  This API, though, has a limit of 30,000 rules that can be created.