The developer of Nano Adblocker (which is a fork of uBlock Origin) may continue working on a manifest v3 compatible adblocking extension for Chromium-based browsers.

https://github.com/NanoAdblocker/NanoCore/issues/238

I look it up but I can't see a clear answer of why?

Manifest V3 doesn’t allow requests to be intercepted and modified by extensions, which is something uBlock Origin requires to block ads and elements on a page.

The proposed way for content blocking in Manifest V3 is how Safari on iOS implemented it a few years ago — a declarative list of URLs to be blocked is provided by the extension and the browser engine looks that up and blocks them. The extension doesn’t see the actual page URLs or requests, leave alone block them.

This is a positive for privacy since the browsing behavior of the user is not exposed to malicious extensions. But uBlock Origin is not some-random-extension-that-wants-to-steal-information. Treating uBlock Origin like any other extension isn’t good. Since Google makes money by selling ads, there will likely not be any concessions on this front.

Manifest v3 still allows browser extensions to observe web requests. It just stops web extensions from blocking them.

There is no win for privacy here.