• X is an entity that can execute some actions on through calling API.
• Each action has its own input model, but one generic controller endpoint as per the following:

[HttpPost("{id}/execute-action")]
 public async Task<IActionResult> ExecuteAction([FromRoute] Guid id,
                                                [FromBody]
                                                [ModelBinder(BinderType = typeof(ActionInputModelBinder))] ExecuteActionInputModel model)
    {
        return await _service.ExecuteActionAsync(id, model);
    }

• All actions input models must use or inherit from ExecuteActionInputModel.

public class ExecuteActionInputModel
{
    [Required]
    public required MyActionEnum ActionName { get; set; }
}

• To be able to bind models at runtime, I am using custom model binder with custom provider as per this link from Microsoft Docs.
• Custom binder:

public class ActionInputModelBinder : IModelBinder
{
    private readonly IDictionary<Type, (ModelMetadata, IModelBinder)> _propertyBinders;

    internal ActionInputModelBinder(IDictionary<Type, (ModelMetadata, IModelBinder)> propertyBinders)
    {
        _propertyBinders = propertyBinders;
    }

    public async Task BindModelAsync(ModelBindingContext modelBindingContext)
    {
            var actionNameValue = modelBindingContext.ValueProvider
                                                      .GetValue(nameof(ExecuteActionInputModel.ActionName)).FirstValue;

            if (actionNameValue == null)
            {
                modelBindingContext.Result = ModelBindingResult.Failed();
                return;
            }

            var actionName = Enum.Parse<RequestActionEnum>(actionNameValue);
    }
}

• The problem is that ValueProvider always returning nulls when using [FromBody] but code execute as expected when using [FromForm].