Creating

public class MainViewModel
{
    private readonly ICustomerDataProvider _customerDataProvider;

    // Using an interface prevents MainViewModel from being tightly coupled to DataProvider
    public MainViewModel(ICustomerDataProvider customerDataProvider)
    {
        _customerDataProvider = customerDataProvider;
    }

    // A collection type that notifies the data binding when items are added or removed
    public ObservableCollection<Customer> Customers { get; } = new();

    public Task LoadAsync()
    {
        if (Customers.Any())
            // Customers were loaded already
            return;

        var customers = await _customerDataProvider.GetAllAsync();

        if (customers is not null)
            foreach (var customer in customers)
                Customers.Add(customer);
    }
}