If you can’t comment on Instagram or use any of the other functions, then your account might have gotten restricted because of breaking one of Instagram’s rules or over following too many people. You can check the rules you agree to by using this app on their website, or if you can’t figure out the issue then you can contact support or customer service. My account got restricted once because of something in my bio. As soon as I changed my bio though the problem was resolved and I could continue using my account like normal. So you could try just deleting your bio first and seeing if you can comment afterwards.