http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/ps/module/guide-pratique-chiffrer-votre-iphone
But before you can turn it on, you need to take a couple steps: enable two-factor authentication for your Apple account if you haven't already, and update all your Apple devices (to at least iOS 16.3, iPadOS 16.3, macOS 13.2, tvOS 16.3, watchOS 9.3, though globally you may need to use a more recent update), or newer.