Chrome Canary finally removes support for Manifest V2 extensions

Download Chrome Canary, enable dev mode, download latest release of Ubo from github, unzip the file, and go into extension page, click “load unpacked”.

I see this error

This is normal since Canary is already v139, and no support.

And why would that be? For example uBlock Origin, which is running on V2 perfectly, what is the issue with it or my good old IDM extension?