Raymond Hill, the developer of uBlock Origin said that "removing the blocking ability of the webRequest API means the death of uBO" in this comment

https://github.com/uBlockOrigin/uBlock-issues/issues/338#iss...

You can follow the issue tracker for any progress related to MV3 development of uBO but from what I can see, there isn't much interest yet in porting uBO to MV3 because it's not worth it.

This EFF article also goes into details about why MV3 is harmful for adblockers.

https://www.eff.org/deeplinks/2021/12/googles-manifest-v3-st...