The APIs usable for adblocking in v3 are extremely limited in scope relative to the equivalents in v2. You can make a v3 adblocker, but it can't have all of the features that e.g. uBlock Origin users have come to rely on such as "cosmetic filtering" (blocking page elements, not just URLs).
>uBlock Origin users have come to rely on such as "cosmetic filtering" (blocking page elements, not just URLs).
Manifest v3 doesn't prevent that. uBlock Origin Lite choose to not require broad permission for every single site, but instead it choose to have the user grant it permission on a site by site basis.
uBlock Origin Lite (https://chrome.google.com/webstore/detail/ublock-origin-lite...) shows what will still be possible under v3.