TempData not showing resultview and returning null - asp.net-mvc

Question

I am having trouble with stored value on TempData, Actually I am learning behavior of TempData and tried with some workable example from various sites.Here is problem : I opening my context file after some linq operation I am saving it to my variable , I used Breakpoint to inspect data,But data is not in TempData. Please can anyone tell me where data will be stored such that I can inspect it using breakpoint of Visual studio.Below is my code
public ActionResult Index()
{
ReadContext db = new ReadContext();
var lst = (from p in db.data1
join f in db.data2
on p.ID equals f.ID
select new
{
Sr = p.Sr,
Group = p.Group,
ID=p.ID,
CompanyName = f.CompanyName
}).ToList()
.Select(x => new dataViewModel()
{
ID=x.ID,
Sr = x.Sr,
Group = x.Group,
CompanyName = x.CompanyName
});
TempData["l1"] = lst;
return View(lst);
}
Including output as image(first beakpoint at Var) ![1]:https://imgur.com/osY345F
Second Breakpoint at TempData ![2]:https://imgur.com/5oIDN9e which is showing me null value is on TempData. What I need to do to see values are visible in breakpoint.

Answer 1

The default TempData provider uses cookies. In order to store an object in TempData you need to serialize it first.
TempData["l1"] = JsonConvert.SerializeObject(lst); //using Newtonsoft.Json;
The amount of data stored in TempData should be minimized. Rather than storing entire records in TempData I would recommend just storing a list of IDs.
Does the application use TempData only sparingly, for relatively small
amounts of data (up to 500 bytes)? If so, the cookie TempData provider
will add a small cost to each request that carries TempData. If not,
the session state TempData provider can be beneficial to avoid
round-tripping a large amount of data in each request until the
TempData is consumed.
[Introduction to session and application state in ASP.NET Core][https://learn.microsoft.com/en-us/aspnet/core/fundamentals/app-state?tabs=aspnetcore2x#tempdata]

Answer 2

var lst = (from p in db.data1
join f in db.data2
on p.ID equals f.ID
select new
{
Sr = p.Sr,
Group = p.Group,
ID=p.ID,
CompanyName = f.CompanyName
}).ToList()
.Select(x => new dataViewModel()
{
ID=x.ID,
Sr = x.Sr,
Group = x.Group,
CompanyName = x.CompanyName
}).ToList();