We’ve heard reports that the Microsoft Teams Meeting Add-in for Outlook on Windows does not show up for some users who have installed the desktop app. There are several reasons why the add-in may no...
Updated Nov 09, 2023
Version 2.0
Blog Post
Just a fyi, in the is transition period you can enable O365 Group right back with AADC (Preview), in doing so Teams will work with onprem exchange mailboxes, while you transition of migrating to EOL. There are some minimum requirements that need to be met here so this a silver bullet at this point.
Configure Office 365 Groups with on-premises Exchange hybrid - Teams with Exchange Onprem
https://technet.microsoft.com/en-us/library/mt668829%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396
Note
Installed a supported version of Exchange on-premises Exchange integration with Office 365 Groups is available in CU1 and newer releases of Exchange 2016, and CU11 and newer releases of Exchange 2013. However, Exchange hybrid requires the latest Exchange 2013 or Exchange 2016 Cumulative Update (CU) to be installed on your on-premises Exchange servers. If you can't install the latest CU, the update released immediately prior to the current CU can be used.
And just back to all my previous points, there is no reason this add-on should be missing, unless the mode hasn't been set at the tenant to "Teams Only" Mode or its been disabled. This is a feature, so if its missing, its most likely been disabled for a reason by the Admin (GA). So please ask you support or tenants admin what the state of Teams is before assuming you have a issue.
Migration and interoperability guidance for organizations using Teams together with Skype for Business - Island
https://docs.microsoft.com/en-US/MicrosoftTeams/migration-interop-guidance-for-teams-with-skype?WT.mc_id=TeamsAdminCenterCSH#coexistence-modes
Hope this helps
Wayne