Oh yeah, at the time there was no support for my current registrar. It was a fun enough project to put my own script together anyways.

This is probably not what you’re looking for, but I found registering a cheap domain name and using a dynamic DNS script that checks every hour or so against your public IP to be a good way to mitigate issues. It also depends on your ISP. Mine typically only renews upon a reboot of the modem or a new PPPoE authentication.

Others have also suggested Tailscale, and I think that’s also a worthwhile option. It’s a pretty easy thing to set and forget, working like any oher VPN client. This is the least complex option to navigate, and if Plex was the only service you were forwarding then it’s likely the best option.

Because you’re serving the website on a non-standard port, you will always need to provide the port in the web browser.

That said, I don’t see anything wrong here. It looks like you’ve got the right ports set, TCP should be correct. You may not get a ping, because ICMP is likely not enabled at the modem. When you ping, you ping the first device that’s exposed to the internet, not an open server.

Just to be sure, when you’re on your phone, you’re using data? If you’re on wi-fi, the modem/router may not be configured to perform NAT reflection, so you won’t be able to access anything via your WAN IP.