Hi Tom N RC,
Welcome to our forum community. Thank you for the posting in our forum community.
Based on the description, we have tested and observed such thing from our end, so we would like to recommend you to kindly make one new folder under
Files tab in team’s General channel and kindly upload PowerPoint document under that newly created folder, after that try to see the result about “Share a PowerPoint” in team meeting.
For creating new folder under team’s
General channel > click your team > click on General Channel > under
Files tab > click on (+) New option > select Folder option, create a new folder and upload PowerPoint document in this newly created folder.


If you need any further help or information, kindly feel free to contact us and provide us some updated information so we can further assist you accordingly.
Regards,
Darpan