Kind of late response, but just so it's documented here step 3 still has to be done for the NGINX server that FreshRSS runs to host the site since this allows the remote user login process to work. FreshRSS has some NGINX config recommendations in their documentation here that I referenced after following the steps quoted and this allowed the reverse proxy to work + removed the network errors I was getting when feeds were being marked as read with my default configs.