I added some additional info to this answer including an additional FAQ concerning the Mobile App in case that's what you are referring to.
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Exactly "how" are you trying to prepare your return? Are you using Online TurboTax with a browser on a mobile device or the Mobile App?
In this minimum system requirements for Online TurboTax (browser version) it shows iOS 9.x under "mobile/other" (the last blue subtopic).
FAQ: TurboTax Online system requirements
While you can use Online TurboTax through a browser, you can't use the Mobile App, however, which requires iOS 10 and above. See this:
FAQ: What are the system requirements for the TurboTax mobile app?