additional fields in the registration menu and MYSQL database

Here's the thing: I need that when I add a new required field in the registration menu, not only the content of this field and the user ID should be stored in the MySQL database, but also the username itself.
Why all this is needed: another server will be connected to the website's user database (what it is doesn't matter) that supports user authentication through the MySQL database, but it needs the usernames and their passwords to be stored in the same database and table in the exact form they are entered.
This is what the field added to the registration menu looks like and directly in MySQL:

I would be very happy if someone decides to help.

You can reply here in the thread or write to my EMAIL dmitrybarynov@gmail.com