Is there any efficient way to get the latest commit of a particular branch using this package?

This question is the continuation of this question, As requested I have raised this as a separate question.

How to check whether a commit is present in a Branch in Azure Dev Ops?

Is there any efficient way to get the latest commit of a particular branch using this package?

The below is a C# demo, it should achieve your requirement:

using Microsoft.TeamFoundation.SourceControl.WebApi;
using Microsoft.VisualStudio.Services.Common;
using Microsoft.VisualStudio.Services.WebApi;
using System;
using System.Collections.Generic;
using System.Linq;

namespace CheckWhetherCommitExistInCurrentBranch
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            Uri orgUrl = new Uri("https://dev.azure.com/xxx/");         // Organization URL
            string project = "xxx";
            string repository = "xxx";
            String personalAccessToken = "xxx";
            string branch_name = "xxx";

            var commitref = GetLastestCommit(orgUrl, personalAccessToken, project, repository, branch_name);

            Console.WriteLine("The latest commit id is: "+commitref.CommitId);

        }

        //get lastest commit
        public static GitCommitRef GetLastestCommit(Uri orgUrl, string personalAccessToken, string project, string repoId, string branchName)
        {
            List<string> branches = new List<string>();
            VssConnection connection = new VssConnection(orgUrl, new VssBasicCredential(string.Empty, personalAccessToken));
            GitHttpClient gitClient = connection.GetClient<GitHttpClient>();
            var commit = gitClient.GetCommitsAsync(project: project, repositoryId: repoId, new GitQueryCommitsCriteria()
            {
                ItemVersion = new GitVersionDescriptor()
                {
                    Version = branchName,
                    VersionType = GitVersionType.Branch
                },
                Top = 1
            }).Result.FirstOrDefault();
            return commit;
        }
    }
}

Works Successfully on my side: