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asp.net cleanest way to pass object to ActionResult

Currently, our application has a lot of ActionLinks that only pass an id to the controller, where the object is retrieved again (that was already present/known on the previous page). Is there any cleaner way to do this, like pass the object instead? As our backend isn't too quick it takes a few seconds to load in the popup which you get after you click on the ActionLink.
I've seen some solutions using ajax to post the object but that doesn't seem like the neatest solution to paste those js lines under/at every ActionLink that is used in combination with a popup.

The #Html.ActionLink() method will generate a url link to the given Controller/Action. Thus, it can only contain parameters that can be contained in the url of the link. So you cannot pass an object through on the url.
If you need to pass through the reference to an object that is stored on the server, then try setting a parameter of the link to give a reference to the object stored on the server, that can then be retrieved by the action (example, the Id of the menuItem in question).
Parameters in the ActionLink are set through the collection that you passed in as the third item in your function call above. Assuming default routing, this would give an address that looks like /Admin/EditPage/?name=XXX where XXX is the value of menuitem.Title. If you included something else here like itemId = menuitem.Id then it would add this as a query string parameter to the url generated, which would then be accessible to the action that is the target of this link.

C# Core MVC How to apply custom URL to controller action

Question:
Edit: It seems my question is actually not a routing issue but an anchoring issue.
If I have assigned a route:
[Route("~/Envelope/List/AcademicYear/{year}")]
public IActionResult AcademicYear(string year)
{
}
How would I correctly use an asp-action to call this route?
using
<a asp-action="List/AcademicYear/" asp-route-id="#Model.AcademicYear">#Model.AcademicYear</a>
returns a url with a %2f (Envelopes/List%2fAcademicYear/2122) instead of / (Envelopes/List/AcademicYear/2122) and thus results in a 404 error
How do I use Custom URL with asp-action to call a specific Action in my Controller?
or
How do I change the routing so I can call an action from a controller with a non default route mapping?
Context:
I've read https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/routing?view=aspnetcore-5.0
and yet i'm still confused on the whole concept of routing and how to interacts with controllers and actions.
In my application I have a controller called Envelope - it controls everything to do with my Envelopes.
I have a class in the Envelopes controller called
public class EnvelopeController : Controller {
public IActionResult List() {... return View()}
and it returns the List.cshtml view. The current url as set by default route mapping: /Envelope/List
In the List.cshtml I have a link that is intended to filter the List on a year parameter
<a asp-action="AcademicYear" asp-route-academicYear="#Model.AcademicYear"> #Model.AcademicYear</a>
My intention is to pass this into a method in the Envelopes controller called "AcademicYear" that gathers the Envelope data stored in temp data, deseralises it and then returns a filtered version based on the parameter:
public IActionResult AcademicYear(string academicYear) { return View("List", newViewModel)}
The return url after this point is correctly: /Envelope/AcademicYear?academicYear=21%2F22
However I would Like to know how to change this so even though I call the Action
<a asp-action="AcademicYear" asp-route-academicYear="#Model.AcademicYear"/>
the URL returned would look like this /Envelope/List/AcademicYear/2122/
Is there a way of doing this? Am I looking at the problem the wrong way? I have thought about simply passing a parameter in the List action and running some form of control to do either set of operations depending on the parameters existence but realistically the List method and the filtering AcademicYear method aren't really doing the same thing and I'd like to seperate out the code into different methods if possible.
Even if its not the appropriate solution I would still like to know if it is possible to change the URL routing for an action after it has been called.
Edit :
I have tried using HttpGet(List/AcademicYear/{academicYear:[a-zA-Z]} however when I do this I can't actually call List/AcademicYear as an asp-action due to the "/" and how that encodes to %2f
Answer:
With the help of the below solutions I realised I was looking at the problem wrong and was actually having issues creating correct anchors.
Reading: https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/routing?view=aspnetcore-5.0#url-generation-and-ambient-values-1
I realised the answer was staring me in the face and I used this alongside the Routes provided for in the answers
<a id="#academicYear.Name" href="#Url.Action("AcademicYear", "Envelope",new {year= academicYear.Name})">

Maybe you just need to decorate your action like that:
[HttpGet("List/AcademicYear/{year:int}")] // or HttpPost it depends on you
public IActionResult AcademicYear(string year) { }

You can add several attribute routes to the action.
[Route("~/Envelope/List/AcademicYear/{year}", Name="ListRoute")]
[Route("~/Envelope/AcademicYear/{year}")]
public IActionResult AcademicYear(string year) { }
and if you need this url
http://localhost:xxxx/Envelope/List/AcademicYear/2021
you can use this html helper, that will create a right anchor tag for you using an attribute route name.
#Html.RouteLink(#Model.AcademicYear, "ListRoute", new { year = #Model.AcademicYear })
I added Name="ListRoute" to the attribute routing (see above)

ASP.NET Core 2.0 URLs

I'm developing a large ASP.NET Core 2 web application but I still get confused with URLs.
When fist learning, I thought URL's took on the name of the View, but discovered they come from the Controller method.
Here is an example to convey my issue:
I have a controller method named Daysheet, which returns a view and model with the same name.
In the Daysheet view, I call various controller methods from Javascript to perform specific actions. One of them is called AssignStaff which takes two integer parameters.
In the AssignStaff method I again return the Daysheet view with model, but now my URL is "AssignStaff"!
I can't just do a redirect because the whole Daysheet model is not being passed to the AssignStaff method.
I have many situations like this where after calling an action, I end up with another URL that I don't want.
UPDATE/EDIT
Thanks for assistance and apologies if my explanation is confusing. I simply have a view called Daysheet that uses a model. I want to call various controller methods to perform various actions, but I want to stay on the "Daysheet" view/URL.
As mentioned, I can't just redirect because in the action method I no longer have the whole model from the Daysheet view. Also, if I redirect I can't pass the whole model because that causes an error saying the header is too long. I think my only choice may be to use ajax for the actions so that the URL doesn't change.

When you just do Return View("") name in a Controller Action, the URL will be the name of the Action you are using.
If you want to redirect to some specific Action, that will help to make sure the Url matches to where you are. You might want to read more about it here.
To do so, use:
RedirectToAction()

The URLs your application responds to are called "routes", and they are either created by convention or explicitly. The default is by convention, of course, which is a URL in the form of /{controller=Home}/{action=Index}. Index is the default action if that portion of the route is left off, so a request to /foo will by convention map to FooController.Index. HomeController is the default controller, so an empty path (e.g. http://sample.com) will by convention invoke HomeController.Index.
Razor Pages have their own conventions. These do somewhat follow the file system, but exclude the Pages part of the path. So a Razor Page like Pages/Foo/MyRazorPage.cshtml, will load up under /Foo/MyRazorPage.
There there is the Route attribute, which allows you to specify a totally custom route. This attribute can be applied to a controller class and individual actions in the class. For example:
[Route("foo")]
public class MyAwesomeController
{
[Route("bar")]
public IActionResult MyAwesomeAction()
{
return View();
}
}
With that, a request to /foo/bar will actually invoke MyAwesomeController.MyAwesomeAction.

Call controller function in cshtml where the string is from a database value

I am trying to have a column in my database where the string stored is:
'"Test count:" + #mycontroller.count()'
And then in my cshtml file do
<li>#Html.Raw(#MenuItem.ItemText)</li>
However, all I am getting displayed is the string in the database and not it the actual result from the controller count() function. How do I get that string to render/execute?

You cannot call a function in a Controller from a view since you don't have an instance of such controller on you view. There are 2 ways of doing what you want:
Having an action on your Controller that given the string you want to use returns the data you require and make an AJAX call to get it
Calculate the data you want before you render the View and pass it in along your model, either using ViewBag|ViewData or as part of your View Model

If understand your intention correctly, you are trying to store C# code in the database and then execute it in your view. That will not (by default) work, since C# is statically compiled language, which means that each change to your code needs to be first compiled to binary code before the code can be executed.
The same applies to MVC razor syntax views (cshtml files) - when a cshtml file is first requested, it is compiled to binary code and then executed.
If you are certain about what you want to do however, there perhaps may be a way, as described in this SO post. But I would first recommend you to describe exactly what it is you are trying to achieve that you ended up with this question.

How to serialize an object in MVC 5 Razor view

I have tried to follow this post in order to create a 3 page form wizard that passes data to each page.
He uses the HTML helper serialize, to serialize an object in the view.
#Html.Serialize("wizard", Model)
However this HTML helper isn't available in MVC 5 it seems.
I found another related post to this here where he suggests using the following to serialize the object.
#Html.Hidden("otherComplexData", new Microsoft.Web.Mvc.MvcSerializer().Serialize(complexObject))
But I then get the following error
There is no argument given that corresponds to the required formal parameter 'mode' of 'MvcSerializer.Serialize(object, SerializationMode)'
It seems to want a SerializationMode, however the documented one doesn't. https://msdn.microsoft.com/en-us/library/microsoft.web.mvc.mvcserializer.serialize(v=vs.118).aspx
What direction can I go in now?
Thanks.

Here's the Serialization option you need:
https://github.com/ASP-NET-MVC/ASP.NET-Mvc-3/blob/master/mvc3/src/MvcFutures/Mvc/SerializationMode.cs
Options are Signed or EncryptedAndSigned.
You can try that and see if it will work.
There's multiple ways to encode data that will work for you. You could put the values in a hidden input using Json.Encode for the view, and Json.Decode on the server side.