Make a httpclient static downloader

I really need help. could someone help me make this codes as static? I got this somewhere here and I've added a little codes. But I've noticed the download process is slow because of not using httpclient as a single instance.

I wanna make this as static so that I can make the httpclient and handler as single instance for all the request.

I have tried to make it static but I failed because I can't trigger the progress percentage and the totalbytes from my main gui form.

Here's the full source code for the downloader.

class Downloader : IDisposable
    {
        private const string UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36";
        private string DownloadUrl { get; set; }
        private string OutputFilePath { get; set; }

        private HttpClientHandler handler;
        private HttpClient client;

        public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);
        public delegate void ProgressChangedHandler2(double? progressPercentage);
        public event ProgressChangedHandler ProgressChanged; //for label progress
        public Downloader(string downloadUrl, string outputFilePath)
        {
            DownloadUrl = downloadUrl;
            OutputFilePath = outputFilePath;
        }

        public async Task StartDownload(CancellationToken token)
        {
            handler = new HttpClientHandler()
            {
                Proxy = null,
                UseProxy = false,
                UseCookies = false,
                //SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls11 | SslProtocols.Tls,
                //ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) => { return true; }
            };
            client = new HttpClient(handler);

            Uri uri = new Uri(DownloadUrl, UriKind.Absolute);

            SetConnection(uri);
            using (var request = new HttpRequestMessage(HttpMethod.Get, uri))
            {
                request.RequestUri = uri;
                request.Headers.UserAgent.ParseAdd(UserAgent);

                using (var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, token))
                {
                    await DownloadFileFromHttpResponseMessage(response, token);
                }
            }
        }
        private async Task DownloadFileFromHttpResponseMessage(HttpResponseMessage response, CancellationToken token)
        {
            response.EnsureSuccessStatusCode();

            using (var contentStream = await response.Content.ReadAsStreamAsync())
            {
                long? totalBytes = response.Content.Headers.ContentLength;
                long totalBytesRead = 0L;
                long readCount = 0L;
                byte[] buffer = new byte[4096];
                bool isMoreToRead = true;

                using (var fileStream = new FileStream(OutputFilePath, FileMode.Create, FileAccess.Write, FileShare.None))
                {
                    do
                    {
                        int bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length, token);
                        if (bytesRead == 0)
                        {
                            isMoreToRead = false;
                            TriggerProgressChanged(totalBytes, totalBytesRead);
                            continue;
                        }

                        await fileStream.WriteAsync(buffer, 0, bytesRead);

                        totalBytesRead += bytesRead;
                        readCount += 1;

                        if (readCount % 10 == 0)
                        {
                            TriggerProgressChanged(totalBytes, totalBytesRead);
                        }
                    }
                    while (isMoreToRead);
                }
                TriggerProgressChanged(totalBytes, totalBytesRead);
            }
        }
        private void TriggerProgressChanged(long? totalDownloadSize, long totalBytesRead)
        {
            if (ProgressChanged == null)
                return;

            double? progressPercentage = null;
            if (totalDownloadSize.HasValue)
                progressPercentage = Math.Round((double)totalBytesRead / totalDownloadSize.Value * 100, 2);

            ProgressChanged(totalDownloadSize, totalBytesRead, progressPercentage);
        }
        private void SetConnection(Uri uri)
        {
            var sp = ServicePointManager.FindServicePoint(uri);
            sp.ConnectionLimit = 20; //default 2 //The number of connections per end point.
            sp.UseNagleAlgorithm = false; //Nagle’s algorithm is a means of improving the efficiency of TCP/IP networks by reducing the number of packets that need to be sent over the network
            sp.Expect100Continue = false; //save bandwidth before sending huge object for post and put request to ensure remote end point is up and running.
            sp.ConnectionLeaseTimeout = (int)TimeSpan.FromMinutes(1).TotalMilliseconds;//60 * 1000; // 1 minute
        }
        public void Dispose()
        {
            client?.Dispose();
        }
    }

And here's the code from my gui

using (var client = new Downloader(url, outputFilePath))
            {

                client.ProgressChanged += (totalFileSize, totalBytesDownloaded, progressPercentage) =>
                {
                    sw.Start();

                    if (tryAbort) { PauseOrResumeProcess(); }

                    PB.Value = Convert.ToInt32(progressPercentage);
                    lvi.SubItems[2].Text = ($"{progressPercentage}%");
                    lvi.SubItems[3].Text = ($"{ Utils.FormatFileSize(totalBytesDownloaded)} of { Utils.FormatFileSize(totalFileSize.Value)}");
                };

                await client.StartDownload(ct);
            }