Additional file-related features and issues within Microsoft Teams for business
Hello Robert G,
Thank you for the update.
You need to meet the following 3 prerequisites to see the Desktop app from the File open preference dropdown menu:
1: You must be using the Teams desktop app for Windows or Mac 2: You download and install the corresponding Office desktop apps (Microsoft Office 2016 or a later version) from the Microsoft 365 portal. 3: You have an Office 365 E3 or E5 license.
I guess that one of the prerequisites isn't met.
See the below link for more details.
https://learn.microsoft.com/en-us/microsoftteams/troubleshoot/files/desktop-app-option-missing
I hope this helps! Let me know if you have any questions.
Best regards, Oluwatosin.