External (SMB) Storage - Offline available? Synced to filesystem of desktop?

I am using an external storage (smb). Is it possible to make “files” (or folders) availabel offline with the desktop sync client? Afaik thos external_folders are not “synced” to the client by default on desktop. On the mobile app I can download files to make them available in offline mode but not on desktop-client?

Is there a setting to make external storage appear in the filesystem of the desktop client (and offline available)?

Thanks for any help with this!

Best regards