Your link has the target="_blank" attribute in your message and opens in a new tab when left clicking on it, so it works, unless I’m misunderstanding something?
On a side note, if I quote your message, it will transform your link as a standard markdown link and trim the target attribute, removing the new tab opening inside the quote.
edit: oh, you edited your message so mine does make little sense now. But still, a manual link with target="_blank" works, and it’s worth noting that there’s also a per-user setting for external links only:
https://meta.discourse.org/my/preferences/interface
