How to upload file AND model using Web API?

There is no formatter that could handle/relate to your ResImageType object. I have once solved a similar problem without a formatter by using a parameter-less method and have processed the data inside the method. For example:

public async Task<HttpResponseMessage> PostFormData()
    {
        if (!Request.Content.IsMimeMultipartContent("form-data"))
        {
            return Request.CreateResponse(HttpStatusCode.BadRequest);
        }

            string upDir= "PathOfDirectory";

            MultipartFormDataStreamProvider streamProvider = new MultipartFormDataStreamProvider(upDir);                
            MultipartFileStreamProvider multipartFileStreamProvider = await Request.Content.ReadAsMultipartAsync(streamProvider);

            // Loop through files.
            foreach (MultipartFileData file in streamProvider.FileData)
            {
                // Save filepaths to DB or do something else
            }
            return Request.CreateResponse(HttpStatusCode.OK);
    }

Similar solution from MS Docs

Another possibility is to create a DTO-like class that is used to transfer the object and use a formatter, for example MultipartDataMediaFormatter seems legit (haven't tried).

You can simply add media and enum at the same time by adding content type in header request.

Content-Type:application/x-www-form-urlencoded

Then try to access file and enum

[HttpPost]
public UploadResponseVm Upload()
{
            //Get enum type
            var enumkey = HttpContext.Current.Request.Form.AllKeys.FirstOrDefault(x => x == "enumkey");
            var enumType = Convert.ToInt32(HttpContext.Current.Request.Form[enumkey]).ToEnum<ResImageType>();

            //Access files
            var postedFileLst = HttpContext.Current.Request.Files.GetMultiple("fileKey").ToList();
}

Use Extension Method to convert to enum

public static T ToEnum<T>(this int param)
{
            var info = typeof(T);
            if (info.IsEnum)
            {
                T result = (T)Enum.Parse(typeof(T), param.ToString(), true);
                return result;
            }

            return default(T);
}

Also verify using curl

curl --location --request POST '{{hostname}}/api/media/addmedia' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--form 'BookLogos=@/path/to/file' \
--form 'enumkey=1'

The following example will solve the issue if you have the following code changes.

Put [FromForm] with parameters

public async Task<ActionResult<Guid>> Create([FromForm] CreateEmployeeCommand command)

and in model

public class CreateEmployeeCommand
{
    public IFormFile FormFile { get; set; }
    public string AnyData { get; set; }
}

Use JS FormData object to POST data to the controller