@gertjan very interesting. Thank you for this.
I was on a few 'premier' captive portals recently - American Airlines/GoGoInflight and a large state university - and I realized that they don't use the 114 option either. It's easy to break the Guest Wifi workflow though with iOS and Mac; just ignore the window the first time. Their Captive Portals don't redirect https either - so you have to know neverssl.com or something similar to get back to the portal.
Returning to the solution and discussion: setting the iOS device to see the 114 option is super easy. However, after I do my auth - the iOS requests again to the url, but now I have no context. I guess this is primarily because the IP address is forwarded from the pFSense. Even if I use Tailscale or Wireguard to get all the devices on the same network - pFSense / Netgate box is forwarding the request, so I can't tell who is coming in based on the iP address, nor mac address.
Am I missing something? After you got the 114 login portal working, how did you redirect the iOS device to a 'captive: false' json? I'm missing that part.