Hello,
If I understand correctly - you can access your authentication app just fine, but you cannot access your Instagram account, is that the case?
If so, this is NOT a Microsoft issue. Think of the authentication app like a key chain. It allows you to add different keys for different houses. If you lose a key, you don't ask the keychain maker for the new key, instead, you will have to work with the house owner to get a new key so you can add it back to the keychain.
Let's say if the keychain itself is broken and you cannot even get to the keychain, then you will work with the keychair maker. That is, if you cannot even start or sign into your authentication app, then it is Microsoft who needs to support it.
But it sounds like you can access authentication app, but you cannot add Instagram account back due to lack of authentication, in this case, only Meta/instagram support can help you. I am sorry.