SMB requires full file system access for shared files on external drive

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On modern macOS versions, Apple enforces strict Transparency, Consent, and Control (TCC) security policies. The built-in file sharing daemon (smbd) requires system-wide disk permission to parse and traverse external volumes safely. Without it, macOS blocks external network access to protect hardware that is not part of the internal boot volume.

To share a specific folder on an external drive without giving total access to your entire file system, configure the volume and user permissions properly: 

Fix External Drive Permissions

• Select your external drive in Finder and press Cmd + I to open the information
• Click the lock icon at the bottom right and enter your administrator password.
• Check the box for "Ignore ownership on this volume" (if available and not used for Time Machine). This allows network accounts to read/write files without matching local POSIX user IDs.
• Alternatively, adjust the Sharing & Permissions list at the bottom of the Info window, adding Everyone or specific groups with Read & Write privileges. 

atsuem wrote:

I am able to connect from my non Apple mobile device to access the shared files. If a shared folder is on an external drive, SMB is not allowed to access these files.

I can only access these files, if SMB has full access to the complete file system.

Why?

There is a separate security protection for external volumes. But since File Sharing can't prompt the remote user for access to an external volume, the only way to allow access is with Full Disk Access.

How can I change it, so that I do not have to active complete access?

You can specify which folders are shareable. Only share the ones you want.