I don’t back anything up but if I did I would use em encrypted usb stick that use anti chip off methods like istorage which coat the flash chips in resin so that if the chips are pulled they damage and I’d use software to encrypt the backups as an extra layer of security.
Or do the same and backup them on to a Blu-ray encrypted.
On the rare chance that I back up my data, I make sure I securely erase the backup after it’s restored to new device and that the backup was encrypted