Available Wi-Fi network notification

Starting with iOS13 there is a new notification that appears "sometimes" when public wi-fi networks are found.

See this screenshot for an example (remove white spaces):
https:// i.imgur.com/MyuGr45.jpg

Since one of our businesses is to manage Captive Portals we would like to know:

1) when this notification appears (since it only appears for certain networks and not always);

2) how can we suggest iOS to show it (e.g. do we need to insert some "magic bit" into access point beacon frames?)
Available Wi-Fi network notification
 
 
Q