I used to be able to embed hotlinks to web pages within comments when I wanted to point to another observation, a BugGuide or Moth Photographers’ Group page, or just about any other url. I don’t know the terminology but I was using either mark-up or html format with carots or brackets, such as,
<url=“https://www.inaturalist.org/people/27047”>My Profile Page, or
the pages in the main iNat site support HTML and Markdown. you appear to be trying to use BBCode, which is not supported on the main site but apparently is supported by Discourse (the platform used by the forum).