I had 2 "Apple Worldwide Developer Relations Certification Authority" certificates. After deleting the older (expired) one in Keychain Access, the error went away in Xcode 13.1.

I'm got the same problem trying to download Xcode 13 RC. I'm in the US, have a developer account, and just downloaded Xcode 13 beta 5 last week and have been using it fine. But I get the same cryptic web page when clicking on the Xcode 13 RC download link. I think this is a mistake and should be telling you that you need to be running macOS 12.X, but it doesn't say that. Here's what the description says: To continue developing apps for macOS Monterey, use Xcode 13 beta 5. But this seems wrong. I believe it should read "To continue developing apps for macOS Big Sur, use Xcode 13 beta 5." Even though the text looks wrong, it's a clue that the requirements have changed. The release notes say "Xcode 13 RC requires a Mac running macOS 11.3 or later." but I believe this is also wrong (likely a copy-paste error that didn't get changed from he previous release notes). IIRC, the final version of an Xcode beta release schedule ("RC") does typically require the new, soon-to-be-released version, so it would make sense for a RC to require macOS 12.X. Xcode 13 Beta-5 has actually been stable for me though, so I'll just continue using it for now.

I agree with @ppix, it's a shame that SceneKit and SpriteKit look to be abandoned (not officially, but it's pretty clear they're not getting much love going forward). With a little more building out and some more comprehensive documentation, these could have been a prefect balance of ease of use and performance. Being able to use them in Swift was wonderful (although I started using them in Obj-C). But yeah, thanks for these APIs, as imperfect as they were, they were great for a while. I found them very useful for writing utility apps, such as for touchscreens used in broadcast.