Having the "All Unreads"(all unread messages in Slack) collected in one place to be handy in Slack.
Set your All Unreads view
From your desktop, click your workspace name in the top left.
Select Preferences from the menu.
Check or uncheck the box next to Show All Unreads.
See screen captures below.
Click on down arrow
Select preferences, and then Show All Unreads
Then All unread (all unread messages) show on the top left: