I ask for some method that prevents the file to even be copied through a disk clone
Oh that’s quite simple! Just don’t have the files on the first disk in the first place. Make them a remote mount from a server, for example via sshfs, webdav, etc. Heck, even ftp if it comes down to it. That way, even though you can clone the disks, you can not get to the files if you don’t also have the full authentication requirements for the remote server (such as a password).
At a conceptual level, you can’t do anything via root to prevent someone who clones the disk from… well, cloning the disk. Having physical access to a disk is a much higher level of access than even root, so if what you are looking for is for your content to not be cloned, you need to fortify physical access to the device.