Hi  @Dochy,

Port forwarding on a router is a technique that is used to allow external devices access to services on private networks. This is typically used for gaming, running a web server, or for some peer-to-peer file sharing systems. The port forwarding feature is only available when the router is working in Router Mode.
You may log in to rotuer's Web management page and go to Advanced > NAT Forwarding > Port Forwarding/Virtual Server/DMZ to configure it. You can set up to 32 entries.
If you are using port forwarding and DMZ host at the same time, please note that port forwarding rules have greater priority than DMZ.
This FAQ provides the detailed instructions on configuring port forwarding based on different router models: https://www.tp-link.com/support/faq/1379/
Additionally, here are some tips for you if port forwarding doesn't work:
    1. Make sure the server is accessible from the internal network.
    2. Make sure your router obtains the public WAN IP address, if your WAN IP is not a public one, port forwarding will not work. (CGNAT address is also private IP address that ranges from 100.64.0.0 to 100.127.255.255.)
    3. Check the firewall settings of your server, make sure it allows traffic from the outside Internet.
You may check more detailed instruction following the FAQ: Why port forwarding feature is not working

In order to better locate the problem, can you provide more details? For example, what are your specific usage requirements and scenarios? Please provide relevant screenshots of the specific settings.

May I know if your network topology diagram is as follows:

Cable modem—router—main deco )))((( client devices

(Note: — stands for wired connection,)))((( stands for wireless connection )