iPhone 11 or Up is required for the new Metahuman Animator as per their blog.
If you want to use an iPhone—MetaHuman Animator will work with an iPhone 11 or later—you’ll also need the free Live Link Face app for iOS, which will be updated with some additional capture modes to support this workflow.
Link to Blog: New MetaHuman Animator feature set to bring easy high-fidelity performance capture to MetaHumans - Unreal Engine