Unable to sign into YouTube App on Apple TV 4K

I’ve tried to log into the YouTube app on my AppleTV 4k.

I’m faced with a blank screen for a few minutes: then get the Sign-in screen.

However?

It refuses to log me in.

Whether I try to scan the QR code, or feed in a code on my phone’s browser, or feed in the code on my Mac’s browser.

I’ve tried turning off the Apple TV, and reset my router, twice.

What’s happening?

How do I solve this?

[Re-Titled by Moderator]