https://old.reddit.com/r/OSINT/comments/n8a30d/instagram_followers/

followers.py

# pip install instaloader

import instaloader

L = instaloader.Instaloader()

# Change for the Instagram profile you want the followers list
profile = "TheZakMan"

# Use your credentials to load session
username = "YourUsername"
password = "YourPassword"
L.login(username, password)  # (login)

# Obtain profile metadata
profile = instaloader.Profile.from_username(L.context, profile)

# Print list of followers
follow_list = []
count = 0
for followee in profile.get_followers():
    follow_list.append(followee.username)
    file = open("followers.txt", "a+")
    file.write(follow_list[count])
    file.write("\n")
    file.close()
    print(follow_list[count])
    count = count + 1