Hey Lionleaf3!
Can you say the version of iOS you’re running? I know until iOS 13 there were issues saving to the Files app.
If you scroll down and hit “Edit Options” is the Files app there and have the red “-“ already?
Also, what options do you see? ICloud Drive and On My IPhone? Are they both greyed out?
I think another valid question is if you use iCloud Photos and the available iPhone, and even iCloud Storage?:
Settings > Apple ID > iCloud > Photos.
Settings > General > iPhone Storage.
Settings > Apple ID > iCloud > Manage Storage.
Hope it works out, let me know what you find if you can! Happy to help if I can, or anyone here.