I thought we fixed this with a redirect already?
In the CP Security page there is a link that goes to https://forums.classicpress.net/c/support/security-page
There is nothing there, it should be redirected to https://link.classicpress.net/forum/security, probably, which then will redirect to https://forums.classicpress.net/c/projects/core-development/18 (suboptimal, given the handle to that link is still “Security”, but better than a 404)
To see the link, go to wp-admin/security.php?tab=developers, then under Support and Documentation, click Security Page forum