Discoure "trydiscourse.com" subdomain doesn't vulnerable

[StaviNahum]

When creating a Discourse account, users receive a subdomain in the format "*.hosted_by_discourse.com". It has been indicated that "trydiscourse.com" may be vulnerable. However, without the ability to obtain a subdomain of this type, it is not possible to take over subdomains such as ".trydiscourse.com".

Is my understanding correct?, or am I missing a method by which a "*.trydiscourse.com" subdomain can be obtained?