Well, I'll just relate my experience.
System Win 7
Using default Windows firewall
IOS device, IPAD 2. Using IOS version Pipboy.
PC gaming machine is on wired ethernet to my router.
IOS device is on Wifi to same router. (of course)
In Windows Firewall I found two Fallout 4 references. One for the launcher which has both internal and external firewall access checked on.
Another entry for the Fallout4.exe located in Steam tree, the game executable itself ...
The first time I ran the game with IOS app enabled, and the in game switch set to yes, I had to go to desktop to find the firewall pop up to click , yes to enable.
That first time the IOS app worked fine.
After I had it rescan for a PC device and it found the PC IP address it needed.
Later after closing game and restarting the IOS app could not find the PC device IP.
I looked at firewall.cpl (firewall control panel) and noted the checkmark for internal network was ON, but external network was OFF.
So I checked external access ON.
Then the IOS pip boy app again found the game pc IP and worked fine.
Now, I did not like the idea of the game having external world access so once the IOS app found the game IP, I went back to the Windows Firewall
and toggled OFF , external access for the Fallout4.exe (game process , not game launcher) This may not be the best course of action, but the IOS
app still managed to work.
I just have to repeat that operation each time I restart the game.
I will also note in my case, since I run 1920x1200 full screen resolution , the pip boy MAP for LOCAL (not world) map has distorted unreadable display, otherwise
is fine.