May I suggest to post this question on a forum better suited to these kind of submissions, like Stack Overflow?<p>This is probably what you’re looking for: <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#attr-target" rel="nofollow">https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#...</a>
Knowing Substack, they might have used the JavaScript window.open() method to do that. But adding target="_blank" to a URL (e.g. <a href="<a href="https://somesite.net" rel="nofollow">https://somesite.net</a>" target="_blank">blah blah blah</a>) also works if you want to go the no-script route