Chromium can be forked (probably there are already a bunch of degoogled ones) to keep Manifest v2

what's missing is social infrastructure to direct attention to this (and maybe it's missing because people are too dumb when it comes to adblockers, or they are not bothered that much, or ...)

and of course, also maintaining a fork that does the usual convenience features/services that Google couples to Chrome is hard and obviously this has antitrust implications, but nowadays not enough people care about this either