Hi @broskobandi
If you are using a 4G conection you are most likley behind a CGNAT. This means that your router is not receiving a publicly available IP address, therfore port forwarding is not possible.
But there are other ways to make services on your local network publicly available like ZeroTier or ngrok, but i have no experience with them. Maybe this thread can help, to point you in the right direction… https://help.nextcloud.com/t/accessing-nextcloud-from-anywhere/113428