I tried your steps and it seems to work: I could access the website just fine, and was brought to the section in the docs. Does this happen in safe mode? Is your forum updated to the most recent version?
Discourse 3.5 was released in August. Lots of things have improved since then.
Since the end of January, there haven’t even been any security fixes for this version, and there have been plenty of them lately.
It’s not linked to Meta. It’s for testing and usually resets once a day, so your account and the posts you created will be gone tomorrow. You can use your Discourse ID if you have one, but otherwise, it’s independent.