This error does not mean that you are signed in or not. The error means that YouTube is asking the Piped proxy to sign in with a YouTube account, probably because it has been detecting quite the weird behavior of a single IP address viewing too many videos at once.
Piped
An alternative privacy-friendly YouTube frontend that is efficient by design.
https://github.com/TeamPiped/Piped
Thanks for the reply. Does that mean that Piped uses a single IP for the proxy and cannot open any videos because of that? That kinda sucks because I really liked this service and it no longer works...
In a very simplified way, yes. That's why I've been thinking we need something more radical, something where different Piped/Invidious servers can talk to each other and bridge between them to appear more distributed.
This sounds like a great idea. How should we contact Piped admins to request this feaure? Does Piped work for you at the moment and what country are you from?
I guess through their repo. It does not work very well, lately, if at all, in all instances I've tried.
My country has no issues with YouTube, if that's your question.
Tangential, may solve anyway:
Yt-dlp gave me that same sign-in error instead of downloading a video. Google flagged something with an IP address, I think, because switching to another one in my vpn and refreshing the browser tab worked instantly.
Tried with Censor Tracker plugin for Firefox. Didn't solve the error, still writes "Sign in to confirm that you’re not a bot".