Hi Daniel,
Unfortunately, this is not something that is supported in Markdown, or in the Parsedown library we are using in AtoM to implement Markdown support.
For static pages, the solution would be just to use HTML, like so:
If you are feeling adventurous and have some familiarity with development (or access to developers and system admins), I did find this Parsedown plugin, which includes support for making links open in new tabs:
Help with installing and configuring this in AtoM is beyond the level of support we can provide via the forum - we haven't tried this ourselves, so if you do, please let us know how it goes!
I got to that plugin from this page, which also includes another code snippet someone else has shared about how they extended Parsedown. This could potentially be a second option to explore:
Finally, I also found a JavaScript solution, here - so this might be something that could be added to AtoM without touching Parsedown? Not sure - again, you'd have to experiment:
Good luck!