Why isn't .then executing on getServer() in Angular 8?

Question

I got the value in the id variable as promise but .then is not responding. Why?

  private  getServer() 
  {
       return  this.db.list('/shopping-carts/').snapshotChanges().toPromise();
  
  } 
 
  private async getOrCreateCartId() //to create a cartid or acceess the cartid 
  {
    let cartId = localStorage.getItem('cartId'); //to create a cartid or acceess the cartid 
    if(cartId) 
    {
      return cartId;
    }
    this.id =   this.getServer()
    .then(result => {
      console.log('From Promise:', result);
      this.cartIdFire = result;
    });
    console.log(this.id);
    console.log(this.cartIdFire);
    if(this.cartIdFire)
    {
      return this.cartIdFire;     
    } 
  }

I am trying to get the value in the cartIdFire, but .then function is not responding. I got the value in the id variable as a promise, though.
i edited this yet this isn't working

private async getOrCreateCartId() //to create a cartid or acceess the cartid 
  {
    let cartId = localStorage.getItem('cartId'); //to create a cartid or acceess the cartid 
    if(cartId) 
    {
      return cartId;
    }
    this.id =   await this.getServer();
    this.id.then(x => this.cartIdFire = x);
    console.log(this.id);
    console.log(this.cartIdFire);
    if(this.cartIdFire)
    {
      return this.cartIdFire;     
    } 
  }

even now all method of my service stopped and cartIdFire is undefined till now
I am new to angular. how do i can set cartIdFire? i see the suggested question but I did not understand anything