Nginx reverse proxy does not respond to internet request

I'm currently in the process of switching our reverse proxy from (a hacky) IIS + ARR to Nginx reverse proxy via Nginx Proxy Manager container on Ubuntu Server 22.04.

I've am able to access the services while inside the LAN both my hostname and IP address, but am unable to do so when coming from the internet. Both ports 80 and 433 have been forwarded and are verified working because I simply changed the destination IP to the new server.

What I've tried:

1. Disabling the host firewall
2. Connecting the container directly to the modem via macvlan and forwarding the ports to it.
3. Ensured that there is no access limitation.

What I've noticed when accessing via the internet: When the ports are forwarded, the browser loads for a while and then fails. When the pots are not forwarded, the browser fails immediately.

This leads me to suspect that NPM is receiving the request but is simply ignoring them.

Any leads as to what configuration I missed?

Your description and analysis is very confused. The first place you should be looking for clues is on the nginx host - if you are running this inside a docker container you've made that job a lot harder. If you are able to connect to the proxy it must have a listening port - this is visible with the 'ss' and 'netstat' commands which will also show active connections. While a browser with developer tools is useful for diagnostics to test basic connectivity you need netcat or similar. Whenever ANYTHING on a server is not as it should be, its logs should be your first port of call. And please do not ask us what is wrong with your configuration when you've not told us what that configuration is.