This is a newish feature that's at least close to what you want https://get.slack.help/hc/en-us/articles/226410907-View-all-your-unread-messages https://get.sla

This is a newish feature that's at least close to what you want https://get.slack.help/hc/en-us/articles/226410907-View-all-your-unread-messages https://get.slack.help/hc/en-us/articles/226410907-View-all-...