I’ve sent a PR to address the get-url issue:
About the 404 on /f/faq and /f/favicon/proxied, when I CURL these routes inside the container, bypassing Nginx, it works. I was able to fix it by changing the location directive described in Serve Discourse from a subfolder (path prefix) instead of a subdomain from location /subfolder to location /subfolder/.
The nav bar showing both Guidelines + FAQ is the expected behavior, it’s unlikely the user will override the faq url with the same url.