EF Core initiate model object without required value

I have a model with some properties, one of which is a User:

public int UserId { get; set; }
[ForeignKey("UserId")]
public UserProfileModel User { get; set; }

And I have some JSON I'm posting up from the browser to a controller action:

[HttpPost("Add")]
public IActionResult Add(MyModel data) //<-- can't get this populated
{
    MyModel model = _service.Add(data);
    return Ok(model);
}

It works great! Except... it immediately errors out, because User is a required field. I am passing the UserId up. If I remove the User field from the model it works.

For context, this is part of a larger application framework with this sort of pattern.

I know I could create a separate Data Transfer Object and map it over to the original Model but that is a lot of extra code and manual configuration for this scenario.

Is there a way to get the Controller action and/or EF Core to somehow instantiate the object and just not be concerned with the User property?

Am I way overthinking this and I should just make User nullable, keeping UserId as the required field?

Example payload:

{
  "title": "Test",
  "content": "Lorem Ipsum Etc",
  "userId": 1,
  "comments": [],
  "topicsIds": [
    29,
    30
  ],
  "topics": []
}