Does this issue persist all the time? Or what changes does this manager do before issue happened?
Does your manager try in other machines?
Does anyone else in your organization have the same issue?
If the manager uploads an Excel file to Teams by himself, could he open it in Teams?
Except the Excel file, try to open other type of Office files, such as word, ppt, etc.
Besides, it recommends you to Perform a clean boot to exclude whether a background program is interfering with Teams.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.