IP Passthrough and Port Forwarding - AT&T Fiber HUMAX BGW320-500 with TP-Link AX11000 as Passthrough Device

I have AT&T Fiber with a HUMAX BGW320-500 modem, and have been having a lot of trouble getting ports to open on this modem. I am primarily trying to assign a custom port in Plex, something other than 32400 to allow remote access for specific family members to view some family photos and footage.

I worked with AT&T Support on this for quite some time, they were unable to assist or resolve and routed me to a 3rd party support team via mobile support that suggested using a 3rd party router with IP passthrough and configure the 3rd party router to handle the forwarding.

I have this configured using the steps from the second comment in the post here: https://community.ui.com/questions/...Question/99786f13-1f76-46dd-9801-7102fd1d44d7

Everything is working, all my wired ethernet devices are working off the new router and Wifi is also working fine. I added two ports to port forwarding in the AX11000 with the specific IP of the machine in question that I want to allow, however it still shows "Not available outside your network" in Plex.

If I use an online port checker such as https://www.yougetsignal.com/tools/open-ports/ - when entering 32400 it shows as open. However my other custom ports 28076 and 36927 are showing as closed. I added some rules in Windows Firewall and checking at command prompt using "netsh firewall show state" I am seeing

It isn't making sense to me that I'm unable to open this port on my standard AT&T equipment, and still unable after following the suggestion from the independent support that AT&T forwarded me to. I have the proof of chat history from AT&T about this issue if needed. I posted this earlier and it appears to have been removed.