How to use dynamic fields at @wire getRecord - LWC (Lightning Web Component)

dynamicFields.js

import { LightningElement, track, wire, api } from 'lwc';

export default class DynamicFields extends LightningElement {
  
  @api recordId;
  @track fields;
  @api objectApiName;
  @wire(getRecord, { recordId: '$recordId', fields: '$fields' })
  record;
  
  connectedCallback() {
    this.fields = this.objectApiName === 'Account'? ['Account.BillingCity', 'Account.Name']: ['Contact.MailingCity', 'Contact.Name'];
  }
  
  renderedCallback() {
    console.log(this.record, 'record');
  }
}