Reverse proxy to another web server behind NAT

I have tried following tutorials and done a lot of experimenting, but can’t seem to forward traffic for one of my domains to a different server on my network. All of the tutorials and discussions I’ve seen are talking about reverse proxies to localhost, rather than another server, so I’m wondering what should be different. Swapping out the localhost ip and/or port [] in those directions for the internal IP and/or port of my other server just causes weird redirect errors.

I have two servers, CYBERserver [] and GAMEserver [] on my NATed network. I have one public IP address (dynamic, unfortunately, but it’s okay). Ports 80 & 443 go to CYBERserver. I host most of my domains on CYBERserver and would like to forward to GAMEserver. How do I accomplish this?

In case these details are important, both servers are on ESXi 7.0 VMs on the same metal. I technically only need port 8080 (not 80 or 443) to go to GAMEserver. Why not just forward that port to that server, you ask? I want to access instead of, so I plan to hide it behind the reverse proxy. And I reverse proxy it on GAMEserver, because ports 80 and 443 go to CYBERserver.

All example IPs, hostnames, and domains changed to protect the innocent.

Also, both VMs are Ubuntu 20.04 LTS server. GAMEserver uses NGINX to serve its panel, I believe.