YouTube 11.49.9 is designed for iOS 12.2 through iOS 14. If you are on iOS 11 or older, you will need an even older version (such as YouTube 10.x).
Google occasionally deprecates older API endpoints. If version 11.49.9 stops playing videos entirely, the API keys embedded in the binary may have expired. This is rare for this version, but if it happens, you must either: Youtube 11.49.9 Ipa