In the modern iOS 9.3.5 landscape, you cannot simply drag and drop an IPA. You must use tools like AltStore or Sideloadly. Here is the review of that experience:
A critical nuance for iOS 9.3.5 users is the existence of "Forever Signed" IPAs. Because iOS 9.3.5 lacks the modern certificate pinning and security hardened in later iOS versions (iOS 12+), certain enterprise certificates or "tweaked" IPAs (often found in third-party stores like AppValley, TweakBox, or Scarlet) tend to work longer or are easier to re-sign. ipa apps ios 935
Note : Free signing lasts 7 days. Paid developer accounts extend this to 1 year. In the modern iOS 9
Thus, refer specifically to application packages built with the iOS 9 SDK or older, signed with certificates that the legacy iOS 9.3.5 kernel still trusts. Because iOS 9