I found a solution.

I grabbed the link for every individual page from the forum, and set the max
internal mirror depth to 1. The number of links was over 29,000. I used a
scraping tool called ParseHub and a Firefox extension called "Click Copy Link"
to speed up this process.

In order to achieve the same appearance of the site offline, I had to add a
couple of external links to the scan rules. To find the necessary external
sites I checked the network GET requests on the Inspect browser tools.

The main one was googletagmanager, which seemed to be responsible for the
site's appearance.