This is to end the potential confusion that can occur when a group used by Teams also appears in Outlook and OWA.

Microsoft issued Office 365 Message Center update MC133135 on March 30 to inform tenants that Office 365 will hide groups created by Teams from Outlook by default. In case you have missed it, the following message appeared on the Office 365 Roadmap recently ( Item ID 26955)… The clutter created by Office 365 Groups adoption across organizations is slowly turning into a problem, and Microsoft is taking the first steps to address the issue. This auto-hide feature didn’t receive much fanfare, and was a much-needed update that most people weren’t aware of - nor do they know how to toggle back on, if needed. The Teams “clutter” also extended over into Outlook, which was frustrating. A couple of the more recent improvements were the addition of the AI-driven, dynamic “hiding” of less-visited teams, and the cross-tenant “Your Teams” view. Initially, your only option was to manually “hide” a team. Since its launch, one of the most frequently requested administration capabilities has been the ability to archive teams - but what most organizations are actually looking for is a way to clean up / organize / personalize the navigation. Within a large organization, for example, with project-based teams, ongoing initiatives, and corporate (HR, finance, etc) teams, an end user could easily become a member of dozens of team workspaces. My perspective: Arguably, one of the biggest complaints about working with Microsoft Teams is how quickly overwhelming the navigation can become for users who create or are members of many team workspaces.

They can be added (one or both) via PowerShell. In the first half of 2018, Microsoft deployed a feature to automatically hide, by default, all new Teams workspaces from the Outlook Global Address List (GAL) and the Groups section within Outlook.

Outlook contact groups not showing up