It's probably because your browser's fingerprint looks too uniform and hard to track. If they could tell who you were, they wouldn't be asking you.

Apparently, YouTube thinks they have a too many viewer problem. This should fix that.

Are you using a VPN?

The only bots we permit are our own and those that pay us for your data

I only ever get this when I'm on a VPN. Sometimes reddit will do that to me too. It means someone's been abusing/scraping YouTube through your VPN server and they've temporarily blacklisted its IP address. Switch your VPN servers or turn off your VPN.

How does signing in prove you're not a bot? Do they not know how many bot accounts there are?

Strong enshittification in this one is.

Ive found that if I turn my router off and on again I dont get this message any more for a few weeks.

I get that sometimes. It goes away when I refresh.

What browser?

Use a youtube frontend. Pipe pipe is the best because it skips sponsor messages and has downloads, followed by Newpipe, Libretube for desktop. Age restricted and paywalled content still requires sign-in unfortunately.