ASP.NET MVC use ViewModels with Services

I'm trying to make a simple Blog-application, but I'm a bit stuck on the architecture of the application.

I'd like to create a details-page with the content of the blog-post and a form for adding comment to the post.

My code looks like the following:

ViewModel

public class PostDetailsViewModel
{
    [ValidateNever]
    public Post Post { get; set; }

    [Required]
    public string Comment { get; set; }

    [Required]
    public string Author { get; set; }
}

Service-layer

public class BlogService {
    public void AddComment(int postId, PostDetailsViewModel model) {
        using(var context = new ApplicationDbContext()) {
            Post post = context.Posts.Include(x => x.Comments).Single(x => x.Id == postId);
                
            Comment comment = new Comment();
            comment.Content = model.Content;
            comment.Author = model.Author;
            comment.TimeStamp = DateTime.Now;

            post.Comments.Add(comment);
            context.SaveChanges();
        }
    }
}

Controller

class BlogController{
    public IActionResult Details(int id)
        {
            PostDetailsViewModel model = service.GetPostDetails(id);
            return View(model);
        }

    [HttpPost]
    [ValidateAntiForgeryToken]
    public IActionResult Details(int id, PostDetailsViewModel model)
        {
            if (ModelState.IsValid)
            {
                service.AddComment(id, model);
                return RedirectToAction("Details", new { id = id });
            }

            return View(model);
        }
}

I already did a lot of research on architectural best-practices, but I can't see the wood for the trees anymore...

Could someone provide me with some best-practices/improvements on my architecture?

Thank you in advance!