Hi Leigh Crookes,
Welcome to our forum! Does the issue occur recently on Outlook Desktop Client?
Did you have any specific operation before the issue occurred?
What is the version of your Outlook? It is recommended that you please check the Outlook client version (File>Office Account>Product Information) and try to upgrade to the latest version to see if the problem is resolved.
Meanwhile, please refer to the article step-by-step Resolve issues with Teams Meeting add-in for classic Outlook - Microsoft Teams | Microsoft Learn
In addition, please check the status of the add-in in Outlook, if you could not find it, you may want to refer to the article: Teams meeting add-in missing from Outlook and new Teams - Microsoft Teams | Microsoft Learn and have a try.
Hope it helps.
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