Trouble getting Remote access

I have yet to manage to get Plex access remotely. I have an AT&T DSL Pace Plc 5031NV-030 modem. It does not support UpnP or NAT-PMP as best I can tell. However, I have port 32400 forwarded for tcp and udp. When I attempt to enable remote access, the green ‘full availability’ message appears briefly then changes to the red ‘not available outside’ message. I have tried disabling the Windows firewall and turned of Defender and Malwarebytes, but still no joy. I have even tried it on a 2nd Windows 10 computer with a static IP with the same results.

I’m thinking it is still a modem issue. AT&T say they are not blocking any ports, yet…

Where do I go from here? I have a 2nd Tomato DD-WRT router available and a VPN account. Could these be of any value in setting up remote access?

Still nogo. I checked for port 32400 open with canyouseeme.org and it shows as open. In my modem DMZ status it shows my server with tcp and udp assigned to the correct public IP. I had to create a custom pinhole with Plex Media Server and the ‘permitted’ application. If that’s not correct, can steer me? Oh yes, Windows Defender firewall has Plex Media Server set for IN and OUT requests.

I finally got one of my 2 test servers working. Not sure what I did to fix it though. The one it is working on is using DHCP. The one that is not working is a static IP. But, obviously, it is not an ISP matter.