question

If you enable the [Store full user IP addresses] in the title settings, the player’s IP address would be contained in the login event -- player_logged_in. If you want to collect the IP addresses for banning players, you can store the IP address in the internal player data that can only be read and written by the server.

In your case, you can set a rule to use login events to trigger a CloudScript function to store the information. To learn more about PlayFab Rules, please check the document -- Actions& Rules quickstart - PlayFab | Microsoft Docs. The CloudScript function that triggered by events can access the events content by accessing the context parameter. Please check this document -- UsingCloudScript actions with PlayStream - PlayFab | Microsoft Docs to learn about how to retrieve the event’s field using CloudScript context. For example, the function could be something like this.

handlers.storeIPaddress = function (args, context) {

    var psEvent = context.playStreamEvent;
    var IPaddress = psEvent.IPV4Address;

    var request = {
        PlayFabId: currentPlayerId,
        Data: {
            "IPaddress": IPaddress
        }
    }
    var result = server.UpdateUserInternalData(request);

    return { result: result };
};

Then you can refer to this doc -- How to get internal player data - PlayFab | Microsoft Docs to get it in your server.