@page "/UploadMvc"
@inject IFileReaderService fileReaderService
@inject HttpClient HttpClient
<h3>Upload multiple</h3>
<input type="file" multiple @ref=inputElement />
<button @onclick="UploadFiles">Upload</button>
<br /><pre>@debug</pre>
@code {
    string debug;
    ElementReference inputElement;
    IFileReaderRef fileReaderReference;
    protected override void OnAfterRender(bool isFirstRender)
    {
        fileReaderReference = fileReaderService.CreateReference(inputElement);
    }
    public async Task UploadFiles()
    {
        var multipartFormDataContent = new MultipartFormDataContent();
        foreach (var file in await fileReaderReference.EnumerateFilesAsync())
        {
            multipartFormDataContent.Add(
                new StreamContent(await file.OpenReadAsync(), 8192),
                "files",
                (await file.ReadFileInfoAsync()).Name);
        }
        var res = await HttpClient.PostAsync(requestUri: "https://myupload.website/api/upload/files", 
                content: multipartFormDataContent);
        debug = await res.Content.ReadAsStringAsync();
    }
}

using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Cors;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
namespace MyFileUploadApplication.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    [EnableCors()]
    public class UploadController : ControllerBase
    {
        [HttpPost("files"), DisableRequestSizeLimit]
        public async Task<IActionResult> UploadFiles(List<IFormFile> files)
        {
            var result = files.Select(file => new { file.FileName, file.Length }).ToList();
            
            return Ok(result);
        }
    }
}