The official YouTube app for Android gets the job done for the majority of users. For everyone else, there are several unofficial alternatives. These apps are for people who hate waiting for features like a Dark Mode. While unofficial apps can be great, they are at the mercy of YouTube. One change and the app can be broken. NewPipe and other apps are experiencing this issue right now.
NewPipe is an open source unofficial YouTube app with a lot of great features. You can select the default video quality, download videos, select the audio format, play videos in an external player, and more. Earlier today, the app stopped working as users got a “Could not decrypt video URL signature” error. It turns out some changes in the YouTube backend are causing the issue, and other unofficial apps are experiencing it as well.
The good news is a workaround is already in the works. The folks over at youtube-dl have figured out a solution and it could potentially roll out to NewPipe later today. This is always a concern with unofficial apps. At a moments notice, they can be completely useless. But the developers of these apps are usually on top of the ball when it comes to changes. A fix can usually be found in a reasonable amount of time. It should be noted that this does not affect YouTube Vanced since that is a mod of the official app, not a separate client.