Everyone can read the analyzed Excel-file

The issue you’re describing highlights a fundamental challenge with how Microsoft Forms and Teams currently handle quiz result files and permissions.

Workarounds:

• Manual Permission Adjustments: As you've found, you can manually change permissions in SharePoint, but this is cumbersome when applied to multiple Teams and ongoing classes.
• Dedicated "Teacher-Only" Folders: Create a specific folder in the SharePoint document library for storing quiz result files. Set permissions so only Team owners (teachers) can access this folder. Move the generated Excel files here after they’re created.
• Automating with Power Automate: Use Power Automate to automatically move newly generated Excel files from the root folder to a designated folder with restricted access. This reduces the manual workload and ensures consistent permission settings.
• IT Department Involvement: Work with your IT administrators to set up standardized templates or policies that can automate permissions for files created by Forms. They could implement SharePoint policies or scripts to manage file placements more securely.

While these workarounds can help mitigate risks, the need for Microsoft to address this issue more directly remains. Your suggestion for preset folders with correct permissions is valid and should be communicated to Microsoft for future updates.

Until a better solution is available, advise colleagues to analyze data without exporting to Excel or follow strict permission checks if they do. Establish a protocol to move sensitive files immediately after creation into secure folders.

Update: Since the Excel-file is placed (by the forms-app) in the root of my Document-library I tried to remove the user rights by stopping permissions inheritance, and the removing the users- and guests-group from the permissions overview. However, this turned of too many rights and gave me more work. For instance, if I make a new channel the documents I place in that channel will not be available for my members unless I grant them permissions to see the files. Again - this can't be the intention of the design, leaving a bunch of users with the work of setting and maintaing user rights in channels/folders. I can't see a way where I can decide where the Excel-file is placed. So - as for now I tell my users NOT to analyze the data in the Excel-file, and that's not the intention - is it?

Review and adjust the permissions of the Teams library to restrict editing and viewing access.

This can be done by:

Going to Teams > Files > Open in SharePoint.

Clicking on Library settings and managing the permissions.

Create dedicated folders for teacher-only files where student data and results can be safely stored.

If you are part of an educational institution, consider reaching out to your IT administrator or support team.

Hope this can help you.