Same issue with Slack. IMO the PRs should be by default opened as drafts, or at least there should be a per repo or per user option to enforce that.
Often someone opens a nonreviewable WIP, or messes up something with branches, and dozens of codeowners get pinged to review a diff of something that was already merged.
Also even if initial PR is flawless, it doesn't hurt for the opener to take a deep breath and self-review it before notifying everyone.
