I have created Queue trigger function with runtime stack .NET 8.0 isolated.

When i send a message from the queue got triggered the function successfully and getting DequeueCount and maxDequeueCount by using below code and configuration.

Function1.cs:

public class Function1
{
    private readonly IConfiguration _configuration;
    private readonly ILogger<Function1> _logger;

    public Function1(IConfiguration configuration, ILogger<Function1> logger)
    {
        _configuration = configuration;
        _logger = logger;
    }

    [Function("Function1")]
    public async Task Run([QueueTrigger("firstqueue", Connection = "AzureWebJobsStorage1")] byte[] queueItem, string id, long dequeueCount)
    {
        // Retrieve MaxDequeueCount from host.json
        int maxDequeueCount = _configuration.GetValue<int>("queues:maxDequeueCount");

        _logger.LogInformation($"MaxDequeueCount: {maxDequeueCount}");
        _logger.LogInformation($"DequeueCount: {dequeueCount}");

        try
        {
            // Your main logic here
            DoStuff();
        }
        catch (Exception ex)
        {
            if (dequeueCount < maxDequeueCount)
            {
                _logger.LogInformation("Handling error, retrying...");
                HandleError1();
            }
            else
            {
                _logger.LogInformation("Max retries reached, moving to poison queue...");
                HandleError2();
            }
        }
    }

    private void DoStuff()
    {
        // Your processing logic here
    }

    private void HandleError1()
    {
        // Handle retry logic here
    }

    private void HandleError2()
    {
        // Handle poison queue logic here
    }
}

Program.cs:

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Configuration;

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureAppConfiguration(config =>
    {
        config.AddJsonFile("host.json", optional: true, reloadOnChange: true);
    })
    .Build();

host.Run();

host.json:

{
  "version": "2.0",
  "queues": {
    "maxDequeueCount": 5
  }
}

local.settings.json:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "AzureWebJobsStorage1": "your-storage-connection-string",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
  },
}

Output:

Assuming you’re using the Azure Functions Isolated Worker Model, you can change the type of your first parameter byte[] queueItem to QueueMessage queueItem

Each message should keep track of their own DequeueCount which is available as property on the QueueMessage: https://learn.microsoft.com/en-us/dotnet/api/azure.storage.queues.models.queuemessage?view=azure-dotnet

The QueueMessageConverter in the Microsoft.Azure.Functions.Worker is taking care of binding the data passed to the function, into the QueueMessage automatically

EDIT:
To get the Value of the maxDequeueCount things will be a little more tricky, but as pointed out in the comments – you could try inject access to the host.json via IConfiguration, as the functionContext does not seem to provide access to those:

var host = new HostBuilder()
.ConfigureFunctionsWorkerDefaults()
.ConfigureAppConfiguration((context, configBuilder) =>
{
    configBuilder.AddJsonFile("host.json", optional: false, reloadOnChange: true); // add this, to get access to host.json values
})
.Build();

and afterwards you could access it by injecting into the function like this:

 public class Function1(IConfiguration _configuration)
 {
     [Function("Function1")]
     public async Task Run([QueueTrigger("%QUEUE_NAME%", Connection = "AzureWebJobsStorage")] byte[] queueItem, string id, long dequeueCount)
     {
         var MaxRetryCount = _configuration.GetValue<int>("extensions:queues:maxDequeueCount");
         try
         {
             DoStuff();
         }
         catch (Exception ex)
         {
             if (dequeueCount <= MaxRetryCount)
             {
                 HandleError1();
             }
             else
             {
                 HandleError2();
             }
         }
     }
 }

I’ll go through the SDK code, to see if there’s a other/easier way – but above should actually work.