Teams Team not showing in Outlook groups - Microsoft 365 group not showing in Outlook groups

Learned something today.

If you create a Teams Team or a Microsoft 365 group, and these were created via Microsoft Teams, they are hidden from Outlook by default.
If you want them to show in both the Outlook left navigation and the address book, you can use Set-UnifiedGroup to flip -HiddenFromExchangeClientsEnabled to $false.

Connect to Exchange Online PowerShell.

To get a group and it's current settings:

Get-UnifiedGroup -id YourGroupName | select displayname,hidden*            
            
DisplayName        HiddenFromExchangeClientsEnabled HiddenGroupMembershipEnabled HiddenFromAddressListsEnabled            
____               ________________________________ ____________________________ _____________________________            
YourGroupName                                  True                        False                         False

To unhide a group:

Set-UnifiedGroup -Identity YourGroupName -HiddenFromExchangeClientsEnabled:$false

Check your adjustment:

Get-UnifiedGroup -id YourGroupName | select displayname,hidden*            
            
DisplayName        HiddenFromExchangeClientsEnabled HiddenGroupMembershipEnabled HiddenFromAddressListsEnabled            
____               ________________________________ ____________________________ _____________________________            
YourGroupName                                 False                        False                         False

Set all groups in your organization to be visible in Outlook:

Get-UnifiedGroup -ResultSize unlimited | Set-UnifiedGroup -HiddenFromExchangeClientsEnabled:$false

Be careful with the last one, if your users have a lot of memberships to Teams the list in Outlook may get very long.