While some sideloading methods work on stock firmware, jailbreaking provides the most seamless experience for iOS 9.3.5. It removes Apple's code-signing restrictions permanently.
Some community-driven sites focus on apps that still work on iOS 9, such as older versions of YouTube, Spotify, and Netflix. How to Sideload IPAs onto iOS 9.3.5 ipa library ios 935 portable
Files are completely free, open-source, and strictly archived for historical preservation. 2. Momentum Store (MTM Dev) While some sideloading methods work on stock firmware,
[Release] IPA Library iOS 9.3.5 Portable - 500+ App Archive for Legacy Devices (iPhone 4s/iPad 2) such as older versions of YouTube
: A PC/Mac application used to install IPA files directly onto the device by "sideloading" them with your Apple ID.