Every version of the YouTube app contains a hard-coded API key. When Google updates its backend (the servers that deliver videos), old app versions send a "handshake" that the server rejects. Even if you sideload the 2016 version of YouTube, the server responds with HTTP 403 Forbidden or a forced redirect to the App Store.
There are generally two types of "exclusive" IPAs floating around the community for this specific iOS version: youtube ipa for ios 935 exclusive
This is the most reliable way to use the "official" YouTube app. It tricks the app into thinking it is a newer version to bypass the "Update Required" block. Fix YouTube on iOS 9.3.5 - newline Every version of the YouTube app contains a
Before you download a random YouTube_Exclusive_iOS935.ipa from a forum link, be aware of the risks. There are generally two types of "exclusive" IPAs