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.