I've looked back at your previous postings about this in February and see that we tried quite a few things.
Can you try one more thing please? Fire up P3D and PF3 and try starting PF3 Web Display on the same PC as PF3 - you should find it as PF3WebDisplay.exe in the PF3_WEB_Display directory under PF3_Displayer.
The reason that I'm suggesting this is that it tries to connect to PF3 using the same interface as pf3_display.exe, but completely different code.
You will see one of two things; if it connects you will see something like this:
2023-05-16 16_52_40-PF3WebDisplay.exe.png (19.98 KiB) Viewed 30777 times
If it fails to connect you will see something like this:
2023-05-16 16_59_49-PF3WebDisplay.exe.png (17.89 KiB) Viewed 30777 times
This will show if the PF3 port is actually available to use; let us know how you get on.
(If you don't have the latest version of Web Display, then it might be an idea to update your copy of PF3 - I notice that you are using 3.16.0)
Regards,
Martin