Microsoft Graph Error : My request is only valid with delegated authentication flow

I have an Azure function (Timer) on .NET 8.0 Isolated that gets files in a one drive folder, but I get this error:

Error: me request is only valid with delegated authentication flow.

I'm using the Microsoft Graph library version 5.61.0.

Code:

private static async Task<GraphServiceClient> GetAuthenticatedGraphClient()
{
    var tenantId = Environment.GetEnvironmentVariable("TenantId");
    var clientId = Environment.GetEnvironmentVariable("ClientId");
    var clientSecret = Environment.GetEnvironmentVariable("ClientSecret");
    var scopes = new[] { "https://graph.microsoft.com/.default" };

    var options = new ClientSecretCredentialOptions
    {
        AuthorityHost = AzureAuthorityHosts.AzurePublicCloud,
    };

    var clientSecretCredential = new ClientSecretCredential(tenantId, clientId, clientSecret, options);

    var graphClient = new GraphServiceClient(clientSecretCredential, scopes);

    return graphClient;
}

public async Task Run([TimerTrigger("0 */1 * * * *")] TimerInfo myTimer)
{
    _logger.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");

    var txtSourceFolder = Environment.GetEnvironmentVariable("txtSourceFolder");
    var graphClient = await GetAuthenticatedGraphClient();
    var driveID = await graphClient.Me.Drive.GetAsync();

    var driveItem = graphClient.Drives[driveID.Id]
        .Items["root"]
        .ItemWithPath(txtSourceFolder)
        .Content
        .GetAsync();

    if (myTimer.ScheduleStatus is not null)
    {
        _logger.LogInformation($"Next timer schedule at: {myTimer.ScheduleStatus.Next}");
    }
}

How can I able to get all files in a one drive folder?