Because this is a third-party modification (a "tweak"), it is not available on the official App Store. It is typically installed as an on non-jailbroken devices or via a repository on jailbroken ones.
: Save videos from your feed and both images and videos from Stories directly to your device, often via a long-press. Facebook & Wolf Hack
: Disable the auto-advance feature in stories and prevent your account from being marked as having viewed someone's story. Because this is a third-party modification (a "tweak"),
: Locate the Wolf for Facebook IPA from a trusted community source like GitHub. Facebook & Wolf Hack
: Supports biometric locking (Face ID or Touch ID) for the app. How to Install and Use (iOS)