Instagram is a total mess in this regard, because the app shows other people’s followers completely at random or based on its own engagement algorithms. If I really need to see the latest updates, I either wait a day or two and check instagram recent followers and get subscription updates through various free online scanners by username, or I just look at mutual friends in Stories. I definitely don’t recommend entering your info into any suspicious apps; it’s better to use regular web checkers that don’t ask for anything, or just not worry about it.