Since this is an older file, it is typically hosted on community-driven archives rather than official stores: Legacy Jailbreak Archives The primary hub for sourcing verified legacy IPAs. Internet Archive (archive.org):
If you still use an iPhone 5s, iPhone 6, or 6 Plus (which cap out at iOS 12), modern YouTube versions lag horribly. YouTube 11.49.9 is optimized for iOS 10.3–12.5. It runs buttery smooth on A7, A8, and A9 chips, whereas modern YouTube 18.x crashes or stutters due to memory leaks from the React Native elements. Youtube 11.49.9 Ipa