Hide 365 Group from Outlook

First we need to connect to exchange online via a Powershell terminal

Connect-ExchangeOnline -UserPrincipalName [email protected]

Then to hide a group from Outlook, enter the following command

Set-UnifiedGroup -Identity "GROUP NAME" -HiddenFromAddressListsEnabled $true -HiddenFromExchangeClientsEnabled

If you would also like to disable the welcome message when added to a group, enter the following command

Set-UnifiedGroup -Identity "GROUP NAME" -UnifiedGroupWelcomeMessageEnabled:$false