That is entirely possible @Stephen. You can see the entire apache config a few posts back plus the additions from @Mark and mine from the last post. As I interpret it, apache is reverse proxying to the uwsgi app, now through http instead of the socket. But I have no idea if that's the right way round. I'm not sure is the config file templates for apache, nginx and uwsgi that you get with the Debian packages are added by the Debian team or if they are there any way and just have been modified to the Debian file layout, but I'd guess either way it's not that likely that they wrote it the wrong way around. But I'm not too experienced to be able to translate the nginx config to apache to see if that would result in something different.
Also, while the nginx config is written as a standalone website, the apache config seems to have been written to just create a /mailman3 site under an existing website, while I use it as a standalone site. So it's entirely possible that I missed something when I modified the website from mailman2 to serve mailman3, but then it shouldn't have been able to show the website at the beginning.