YouTube Plus supports iOS 14 and above. However, if you're sideloading it on a non-jailbroken device, you must also consider the YouTube app's compatibility with your iOS version. Below is a list of the latest supported YouTube versions per iOS:
Here are some possible options:
Until this issue is resolved, it is recommended to use YouTube version 20.14.1 or below.
Before jumping to conclusions, let’s clarify a few things:
The issue seems to lie somewhere in the sideloading process itself, even without any tweaks applied. It might be related to an invalid or missing VisitorID or VisitorData, as suggested here. This error has become more frequent due to YouTube’s stricter anti-download measures.
Possible temporary workaround: