Modified versions like YouTube++ are popular for legacy devices because they offer background playback and ad-blocking. How to Install and Fix YouTube on iOS 10.3.4
For users running on legacy devices like the iPhone 5 or iPad 4, installing a functional YouTube app requires specific workarounds. Official support for these versions has ended, but you can still access content using historical IPA files, App Store "last compatible" tricks, or jailbreak modifications. Where to Find YouTube IPA for iOS 10.3.4
The Internet Archive's Google LLC Collection hosts a comprehensive library of legacy YouTube IPAs.