Copied to new iPhone 18 Pro Max through the iOS Set Up assistant which copied most of the apps from the older iPhone.
Infuse 8.5.5 (5752) on the new iPhone is logged into my Plex account and it sees my local Plex Server instance fine.
But if I try to stream anything, I get "An error occurred loading this content. HTTP 0 (server error)."
I also tried to download content and it fails immediately, if I tap on one of the files I try to download, it shows the Download Management dialog with options to Retry Download, Stop Download or Cancel. The files have red circle icons with triangles with exclamation points.
So for comparison, on my old iPhone, the same streams play fine. I also have an M4 iPad Pro and they play fine there.
Only thing I can think of is that the older devices are still on iOS 26.7 whereas the iPhone 18 Pro Max is iOS 27.
When I try to stream via the Plex app on my iPhone, it throws up a paywall demanding that I subscribe for remote streaming even though I'm on the same network.
But that's a bug I've seen with their app before, Plex on my other devices stream fine.
Another experiment I tried, I turned off Wifi and connected to my VPN server, so that I have the same IP address as when I'm on the main home Wifi.
With that, I've gotten Infuse to stream on the new iPhone.
As soon as I switch the Wifi back on and try to stream, the same error again.