Problem solved!
It looks like the file and/or folder permissions did not match.
The trick was/is to create the required folder via WinSCP. Then the backup works.
I would assume that there is a "problem" with the rights assignment or management. Perhaps the sftp server called up by the openSSH server under Windows has its own or at least a strange rights management. And the OPNsense cannot cope with this.
Anyone who can describe this in more detail is welcome to comment.
It looks like the file and/or folder permissions did not match.
The trick was/is to create the required folder via WinSCP. Then the backup works.
I would assume that there is a "problem" with the rights assignment or management. Perhaps the sftp server called up by the openSSH server under Windows has its own or at least a strange rights management. And the OPNsense cannot cope with this.
Anyone who can describe this in more detail is welcome to comment.