Hi @Irfan Khan
Welcome to our forum!
Based on my research, it takes some time to display after joining a group, it is recommended that please restart the Outlook or OWA after the operation to see if the issue persists.
If the issue persists, as i know, Microsoft introduced a change to "hide" all Teams-enabled groups form Outlook to reduce confusion. In addition, i found a similar thread that many people find it useful, it mentioned that the fix is to toggle the 'Hidden From Exchange Clients Enabled property' via PowerShell: Set-UnifiedGroup Team688 -HideFromExchangeClients:$false.
More information SOME Teams not showing up in Groups within Outlook - Microsoft Community
Hope it helps!
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