Post: https://medium.com/p/4ba9dd724e55

WKWebView-RemoveFacebookCookies.cs

public static void RemoveFacebookCookies()
{
    var websiteDataTypes = WKWebsiteDataStore.AllWebsiteDataTypes;
    WKWebsiteDataStore.DefaultDataStore.FetchDataRecordsOfTypes(websiteDataTypes, (NSArray records) =>
    {
        for (nuint i = 0; i < records.Count; i++)
        {
            var record = records.GetItem<WKWebsiteDataRecord>(i);
            if (record.DisplayName.Contains("facebook"))
            {
                WKWebsiteDataStore.DefaultDataStore.RemoveDataOfTypes(
                    record.DataTypes,
                    new[] { record },
                    () =>
                    {
                        Debug.WriteLine($"deleted: {record.DisplayName}");
                    });
            }
        }
    });
}