port forwarding

Recently due to some connection issue where my speeds would go down from 40 mbps to 2-3 mbps after half an hour of restarting the router, the Airtel technicians changed my router from the Nokia ONT to a Zyxel PMG5617-R20B. There's an option to forward ports inside this router's configuration...

I have a jio fibre router. This is connecte to a TPlink mesh (M5). Anybody able to port forward from the jio router? The IP shown in the jio router is different from the public IP. I have very limited knowledge on this and my friend says I have get a static IP to connect my laptop in home from...

What I am trying to do - I need to setup a web server that will run on raspberry pi. The server will use custom port. And one of route will have incoming data from internet Issue I'm facing - ACT ISP uses a CGNAT. So impossible to setup port forwarding What options do I have ? Please also...