In Slack, there are two usernames that users can give, a full name and a display name.
While the full name is mandatory the display name is entirely optional.
In the default tweaks tab, punch the Expand button for the Name display tweaks.
Click Expand next to Name display in the default controls tab.
Tick the checkbox labelled Show full names instead of display names, then click Save.
In some workspaces, especially corporate ones, display names may be viewed as too informal.
