EF Core: The entity type 'List<Course>' was not found. Ensure that the entity type has been added to the model

I am trying to update columns in the database for a Courses table, but get the following error:

> The entity type 'List<Course>' was not found. Ensure that the entity type has been added to the model.

Basically I'm trying to get the state of the check boxes. For example if a course is selected for an Instructor as an author of that course, then enter the instructor's Id into the Course.AuthorId

Here is the method in the controller

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> EditInstructorCourse(int id, List<EditInstructorCourseViewModel> model)
{
        if (_context.Courses is null)
        {
            return NotFound();
        }

        var courses = await _context.Courses.ToListAsync();

        try
        {
            for (int i = 0; i < model.Count; i++)
            {
                if (model[i].IsAuthor = true)
                {
                    courses[i].AuthorId = id;
                    _context.Update(courses);
                }
                else
                {
                    courses[i].AuthorId = null;
                }
            }

            _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            throw;
        }

        return RedirectToAction(nameof(Index));
}

Here is the view model

public class EditInstructorCourseViewModel
{
    public string CourseId { get; set; }
    public string CourseName { get; set; }
    public string CourseAuthor { get; set; }
    public string CourseEditor { get; set; }

    public bool IsAuthor { get; set; }
    public bool IsEditor { get; set; }
}

The model classes:

public class Instructor
{
    public int Id { get; set; }

    [DisplayName("Instructor")]
    public string InstructorName { get; set; }

    [ForeignKey("AuthorId")]
    [DisplayName("Author Of")]
    public ICollection<Course> CoursesAuthored { get; set; } = new List<Course>();

    [ForeignKey("EditorId")]
    [DisplayName("Editor Of")]
    public List<Course> CoursesEdited { get; set; } = new List<Course>();
}

public class Course
{
    public int Id { get; set; }

    [DisplayName("Course")]
    public string CourseName { get; set; }

    public int? AuthorId { get; set; }
    public Instructor? Author { get; set; }
    public int? EditorId { get; set; }
    public Instructor? Editor { get; set; }
}

Fluent API

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Course>()
        .HasOne(course => course.Editor)
        .WithMany(editor => editor.CoursesEdited)
        .HasForeignKey(course => course.EditorId);

    modelBuilder.Entity<Course>()
        .HasOne(course => course.Author)
        .WithMany(editor => editor.CoursesAuthored)
        .HasForeignKey(course => course.AuthorId);
}

And the view

@model List<OneToManyMany.Models.ViewModels.EditInstructorCourseViewModel>

@{
    var instructorId = ViewData["InstructorId"];
    var instructorName = ViewData["InstructorName"];
}

<h2>Edit Courses for <strong> @instructorName</strong></h2>


<div class="form-group">
    <label asp-for="@instructorName" class="control-label"></label>
    <input asp-for="@instructorName" class="form-control" />
    <span asp-validation-for="@instructorName" class="text-danger"></span>
</div>

<div>
    <form asp-action="EditInstructorCourse" method="post">
        <div asp-validation-summary="ModelOnly" class="text-danger"></div>
        <input type="hidden" asp-for="@instructorId" />
        <div class="form-group">
            <h5>Author Of</h5>
            @for (int i = 0; i < Model.Count; i++)
            {
                <div class="form-check m-1">
                    <input type="hidden" asp-for="@Model[i].CourseId" />
                    <input type="hidden" asp-for="@Model[i].CourseName" />
                    <input asp-for="@Model[i].IsAuthor" class="form-check-input" />
                    <label class="form-check-label" asp-for="@Model[i].IsAuthor">
                        @Model[i].CourseName
                    </label>
                </div>
            }
        </div>
        <div class="form-group">
            <h5>Editor Of</h5>
            @for (int i = 0; i < Model.Count; i++)
            {
                <div class="form-check m-1">
                    <input type="hidden" asp-for="@Model[i].CourseId" />
                    <input type="hidden" asp-for="@Model[i].CourseName" />
                    <input asp-for="@Model[i].IsEditor" class="form-check-input" />
                    <label class="form-check-label" asp-for="@Model[i].IsEditor">
                        @Model[i].CourseName
                    </label>
                </div>
            }
        </div>
        <div class="mt-4">
            <a asp-controller="Instructors" asp-action="Index" asp-route-id="@instructorId" class="btn btn-secondary me-2">Cancel</a>
            <button id="saveBtn" type="submit" class="btn btn-primary">Save</button>
        </div>
    </form>
    <hr />
</div>

Any help would be greatly appreciated.

To update the entity: you need to get the entity, update the value and call SaveChangesAsync. No need to call update in your case. Just remove it as suggested by @ivan