Go to your Instagram profile, open the 3 lines ( ☰ ) in the upper right part of the screen, tap on Settings and Privacy and scroll down to Account privacy where you turn on a Private Account. That is it, only the people who are approved can see your posts.
It’s super easy, I did it myself recently. Just open Instagram, go to Profile → Menu (☰) → Settings and privacy → Account privacy, then turn on Private account, and you’re done.
