Short answer. Instagram account banned after login means the password worked and the next screen was a disable or suspension. Screenshot that second screen. Appeal from its button. A successful password does not mean the account is clear.
Instagram account banned after login is a two-step moment. The password is accepted. The next page says the account is disabled, suspended, or permanently disabled. People close the app and think the login failed. The second screen is the case. Screenshot it.
If a login alert arrived just before the ban, the account may have been compromised. Save that email and follow Instagram hacked recover alongside the appeal. Do not send the password to someone who says the “after login” screen is a bug they can clear.
Try the website if you only saw the notice in the app, and the app if you only saw the website. If both show the same sentence, file that sentence. Send the username and the screenshot. We use Meta’s own official channels, open support chats, send follow-up emails, and push the case hard until it gets looked at. It takes a few days. Start a case on the contact page. How it works is the three steps. We never ask for your password.