To add a new function, remove --language c# in the command func new --language c# --template "Timer trigger" --name UpdateApplications.

I have created the Timer Trigger .NET 8.0 isolated Azure function using below commands:

1. func init --worker-runtime dotnet-isolated --target-framework net8.0 --docker
2. func new --template "Timer trigger" --name UpdateApplications

local.settings.json:

{
    "IsEncrypted": false,
    "Values": {
        "AzureWebJobsStorage": "UseDevelopmentStorage=true",
        "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
    }
}

UpdateApplications.cs:

public class UpdateApplications
    {
        private readonly ILogger _logger;

        public UpdateApplications(ILoggerFactory loggerFactory)
        {
            _logger = loggerFactory.CreateLogger<UpdateApplications>();
        }

        [Function("UpdateApplications")]
        public void Run([TimerTrigger("0 */5 * * * *")] TimerInfo myTimer)
        {
            _logger.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");
            
            if (myTimer.ScheduleStatus is not null)
            {
                _logger.LogInformation($"Next timer schedule at: {myTimer.ScheduleStatus.Next}");
            }
        }
    }

Program.cs:

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureServices(services => {
        services.AddApplicationInsightsTelemetryWorkerService();
        services.ConfigureFunctionsApplicationInsights();
    })
    .Build();

host.Run();

Response:

Functions:

        UpdateApplications: timerTrigger

For detailed output, run func with --verbose flag.
[2024-09-06T09:20:14.269Z] Host lock lease acquired by instance ID '000000000000000000000000F72731CC'.
[2024-09-06T09:25:00.107Z] Executing 'Functions.UpdateApplications' (Reason='Timer fired at 2024-09-06T14:55:00.0494065+05:30', Id=913778fb-b3a2-496b-a53a-158293318108)
[2024-09-06T09:25:00.243Z] Next timer schedule at: 9/6/2024 2:55:00 PM
[2024-09-06T09:25:00.243Z] C# Timer trigger function executed at: 9/6/2024 2:55:00 PM
[2024-09-06T09:25:00.273Z] Executed 'Functions.UpdateApplications' (Succeeded, Id=913778fb-b3a2-496b-a53a-158293318108, Duration=211ms)