Can you explain further what you mean by "pending actions on them"? We are working to simplify and streamline our notifications and todos in GitLab. In particular, the current thinking is that they are very similar. A "notification" is an email, and a "todo" is a something that GitLab calls your attention to in the Web UI to take action on. So mechanically, they are very similar and we would like to harmonize them.
Our latest discussion is in https://gitlab.com/gitlab-org/gitlab-ce/issues/48787.