Predefined Fields and problems saving data in WordPress Manager

I write because I have a problem with the user registration and available fields. Within the fields available when accessing the users of the WordPress Manager appear a series of fields (the default) and three more that we have added to the database and are there to enter the information.
The problem comes when trying to modify the Ultimate Member registration form. It has a very intuitive and useful interface, the point is that when adding a new field to the form, between the fields Predefined Fields are not the fields that I have inside WordPress users, which I have to do with the Custom Fields and these are not added to the new user’s data.
Also when using a field of Predefined Fields it is already marked as not available when you put another field to the form, something that indicates that that field is of the database.
This is my question, can I use fields from the user database in the registration form, different from the Predefined Fields, and that this data be saved in the user profile of WordPress?
Thank you very much in advance.