C# Sample to capture version of Document Sets using CSOM in SharePoint Online. It also lists out all the Document Set content type items along with the version information from a document library using the latest CSOM library released recently (version: 16.1.20317.12000 or above).

VersionDocumentSets.cs

using Microsoft.SharePoint.Client;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security;
using System.Text;
using System.Threading.Tasks;

namespace CSOM.ConsoleApp.Sample
{
    class Program
    {
        static void Main(string[] args)
        {
            string userName = "MeganB@contoso.OnMicrosoft.com";
            SecureString password = ConvertToSecureString("password");
            var ctx = new ClientContext("https://contoso.sharepoint.com/sites/ModernTeamSite");
            ctx.Credentials = new SharePointOnlineCredentials(userName, password);
            ctx.Load(ctx.Web);
            ctx.Load(ctx.Web.Webs);
            ctx.ExecuteQuery();
            Console.WriteLine(ctx.Web.Title);

            var list = ctx.Web.Lists.GetByTitle("Documents");
            //var item = list.GetItemById(26);
            //ctx.Load(item, l=>l.ContentType);
            var query = new CamlQuery()
            {
                ViewXml = String.Format("<View><Query><Where><Eq><FieldRef Name='ContentType' /><Value Type='Computed'>Document Set</Value></Eq></Where></Query></View>")
            };
            ListItemCollection items = list.GetItems(query);
            ctx.Load(items);
            ctx.ExecuteQuery();
            foreach (var item in items)
            {
                Console.WriteLine("Item id: "+ item.Id);
                var folder = item.Folder;
                ctx.Load(folder);
                var ds = Microsoft.SharePoint.Client.DocumentSet.DocumentSet.GetDocumentSet(ctx, folder);
                ctx.Load(ds);
                var dsVersions = ds.VersionCollection;
                ctx.Load(dsVersions);
                ctx.ExecuteQuery();
                Console.WriteLine("Version count: "+ dsVersions.Count);

                //Add new version. First parameter signifies whether to capture items within docset with their major or minor versions checked in. Second parameter is a string/comment.
                dsVersions.Add(true, "capture new version thru CSOM");
                ctx.ExecuteQuery();

                //To get contents of a captured version of a Document set along with the site columns (fields) for the library.
                List<Microsoft.SharePoint.Client.DocumentSet.DocumentSetVersionItem> itemsWithinDS = (List<Microsoft.SharePoint.Client.DocumentSet.DocumentSetVersionItem>)dsVersions[0].GetDisplayContents();
                List<Microsoft.SharePoint.Client.DocumentSet.DocumentSetVersionField> fields = (List<Microsoft.SharePoint.Client.DocumentSet.DocumentSetVersionField>)dsVersions[0].GetDisplayFields();
                ctx.ExecuteQuery();
                Console.WriteLine("Contents count: " + itemsWithinDS.Count);
                Console.WriteLine($"Field title: {fields[0].Title}, Value: {fields[0].FormattedValue}");
                
                //break;
            }

            ctx.Dispose();
            Console.ReadLine();

        }

        private static SecureString ConvertToSecureString(string password)
        {
            if (password == null)
                throw new ArgumentNullException("password");

            var securePassword = new SecureString();

            foreach (char c in password)
                securePassword.AppendChar(c);

            securePassword.MakeReadOnly();
            return securePassword;
        }
    }
}