This usually means the "certificate" has been revoked. You will need to delete the app and re-install it via AltStore or Sideloadly.
A fork of the original YouTube app that allows for extensive customization of the user interface. How to Install Updated (.upd) IPAs youtube 15021 ipa download upd
: A standard YouTube IPA is usually between 100MB and 150MB . If the file is tiny (e.g., 5MB) or massive (e.g., 500MB+), it is likely a virus or fake. This usually means the "certificate" has been revoked
When you search for "YouTube 15.21.1 IPA download," you will find dozens of shady websites, ad-filled link shorteners, and potentially malicious file hosts. 5MB) or massive (e.g.