As part of the introduction of workspaces in 2023, we no longer offer the default Team Inbox for team workspaces on the Starter or Business plan.
If you had a Team Inbox before, it has become a regular project in your team workspace that you can rename and edit in any way you like. It’s still shared with all of your current team members, however, new workspace members will no longer be added to the project automatically.
If you still want to see your Team Inbox permanently in your sidebar, you can simply add it to your favorites.