They've implemented V3. What they're not doing is removing support for V2, so plugins that want the full access can do so.
All I can find is:
We have not yet set a deprecation date for Manifest v2 but expect it to be supported for at least one year after Manifest v3 becomes stable in the release channel.
https://blog.mozilla.org/addons/2021/05/27/manifest-v3-updat...
So they will eventually remove it sooner than later.