Running into the same issue as stated above. This started recently—first noticed it yesterday (11/4/2020). Up until then, I had been able to access Realms just fine, but now I can’t see any of them. The web address in the error message goes to an article about troubleshooting accessing Realms from a child account, which is not the type of account that I have.
Thanks, John, for the comment. The first thing I did was check my gold subscription, but turns out I must have been looking at it wrong because when I checked again, I saw that it had ended right about when the issue started happening. I got that squared away, and it’s working fine now.