how to remove system data & ios on iphone Xs max taking 48GB on a 64GB phone

Did you already try to set your iPhone back to factory settings and restore from the latest backup?

Restore your iPhone, iPad, or iPod to factory settings using a computer - Apple Support

If you don't have a recent iCloud backup, you will have to reset the password as explained in this article, but won't be able to use the old backup anymore:

If you can’t remember the password for your iPhone, iPad, or iPod touch encrypted backup - Apple Support

What encryption code?

Is this phone linked to your AppleID?