Oh! It's right there in the page's HTML header.
Code:
<link rel="alternate" type="application/rss+xml" title="AppleNova Forums Recent Threads" href="external.php?type=RSS2" />
<link rel="alternate" type="application/rss+xml" title="AppleNova Forums Recent Posts" href="external.php?type=RSS2&lastpost=true" />
So:
https://forums.applenova.com/external.php?type=RSS2
https://forums.applenova.com/externa...&lastpost=true