// Startup.cs 

public void ConfigureServices(IServiceCollection services) 
{
    ...
    services.AddCrmWebApiClient();
    ...
}

// AccountController.cs 
...
using System.Threading.Tasks;
using CrmNx.Xrm.Toolkit;
using CrmNx.Xrm.Toolkit.Query;
...

[ApiController]
public class AccountController : ControllerBase
{
    private readonly ICrmWebApiClient _crmClient;

    public AccountController(ICrmWebApiClient crmClient)
    {
        _crmClient = crmClient ?? throw new ArgumentNullException(nameof(crmClient));
    }
    
    [HttpGet]
    public async Task<IActionResult> GetAccounts(CancellationToken cancellationToken)
    {
        // await _crmClient.RetrieveMultipleAsync("account") - Retrieved all fields
        var collection = await _crmClient.RetrieveMultipleAsync("account", QueryOptions.Select("fullname"), cancellationToken);
        
        return Ok(collection.Entities);
    }
}