This issue may occur because OneDrive accesses files during its syncing operations, which can cause them to appear in your recent files list even if you haven't opened them manually.
Another possible cause is that certain applications or system processes may access files for indexing or scanning purposes, leading to their inclusion in the recent files list.
It's also important to review the apps and services you've granted access to your files. To check this:
- Go to the Apps and Services section of your Microsoft account.
- Review the list of apps with access to your account and files.
- Click "Edit" to view and manage the permissions you've granted. If you’ve unintentionally granted access to a questionable or "rogue" app, it may have access to your files.
It is concerning that Microsoft has not provided a clear explanation for this issue. If this is a significant concern, particularly for those in Europe, consider leveraging GDPR (General Data Protection Regulation). Under GDPR, you have the right to request details about who has accessed your files, especially if they contain personal data or are tied to your Microsoft account. For more information, you can visit Microsoft Privacy Support. There are number of law for US citizens depending on which State you live in.