Installing the YouTube app on iOS 9.3.5 is challenging because official support ended years ago. However, you can still get it working by downloading the (v13.42.6) through your account's purchase history or by using community-developed fixes like TubeRepair for jailbroken devices. 1. Downloading the Last Compatible Version (No Jailbreak)
That's it! You should now be able to launch the YouTube app on your iOS device. youtube ipa file for ios 9.3.5
This is the safest and most reliable method if you have previously downloaded YouTube on your Apple ID. Installing the YouTube app on iOS 9