Update :slight_smile
It was a problem of rights when the hard disk is automatically muonted by the pi, i can’t change them. I also manually mounted it following these instructions https://retroresolution.com/2016/06/10/automatically-mounting-an-external-usb-hard-disk-on-the-raspberry-pi/, then changed the rights.
After this i modified the owner so that nextcloud can use it : You don’t have permissions to upload or create files here - local (external ntfs-3g storage)
It works!