Hi John7100,
Greetings
Thank you for posting in Microsoft 365 Community forum.
Apologies for the inconvenience caused, may I know what version of Outlook are you using and when did you start to notice the change?
From your post description I presume you are using Outlook for Mac, please correct me if I am wrong. To insert your signature press Alt+N, A, S. If the issue persists kindly share more information with me including your Outlook version. You mentioned that Outlook listed in the Office 365 Apps dropdown kindly shed more light on this.
Looking forward to your reply so we can assist you further. Your kind understanding is highly appreciated.
Kind regards,
Simbarashe