Have you logged it with Meta?

Received a further email overnight from "Meta Store Support's specialized team" so it does look like they're looking at the issue.

I sent the link to this forum post in the chat so they could see others are having the same issue.

Just had an online support chat, the operative has escalated it to higher support who will get back to me in 3-5 days apparently.

Having the exact same issue. My son just got a Quest 3 for his 11th Birthday. I've created a parental account added him as child online but when I try add his account to the headset which then sends him a link to log in via the app he's unable to get...