Apple ID invalid or no supported

Hi, 2 years ago I bought a new iphone and created a new Applie ID, and tried to get rid of the old ID (if I remember correctly). I have kept the old iphone (iphone 7) which is connected to the old ID.

I want to use the old iphone and I am trying to use the new ID, but it brings me back to the old ID.

I tried to reset the password for the old ID, but it eventually lead me to resetting the password of the new ID on the new phone.

I tried to reset the whole iphone setting (old phone), but again it is requiring me to sign in to the old ID first. I tried again and at some point, I received the message : Apple ID is invalid.

I understand that the ID has been deleted (intentionally) or deactivated since I have not used the phone for quite a while now, but the problem is that I cannot change the ID to the new one and so cannot use the different functions of the old iphone or update the phone and the apps.

what can I do in this situation?! :(

Many thanks for any help or tips!