Posting this at least for info purposes, with a slight hope that perhaps this can be fixed within PureBrowser.
- behavior on PureBrowser in PureOS: I see the Apache 2 Test Page on CentOS
- behavior in every other browser, in PureOS, or other OSes on the same machine (Firefox, Brave, Epiphany, emacs web browser, whether in PureOS or macOS): I see the actual website (which is about a comic and some role-playing games)
With help from the Matrix chat, we've tracked this down to the user agent.
When I changed it to, for example.
"Mozilla/5.0 (Linux; Android 6.0.1; KIW-L21) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.143 Mobile Safari/537.36"
I was able to see the site.
Even with eww, whose user agent is: "URL/Emacs Emacs/26.1 (X11; x86_64-pc-linux-gnu)", I'm able to view the site normally..
I know this is more a matter of the web host handling of user agent, however perhaps the PureBrowser user agent could be tweaked somewhat for better compatibility? Otherwise, at least the issue is out here and might be helpful to someone else experiencing a similar issue on other websites.