Uploading files to SharePoint OnPremise 2016 using .NET Core 5.0 and HttpWebRequest C# - .net-core

Question

SharePoint CSOM is not supported in .NET Core 5.0, so I'm trying to use HttpWebRequest to upload files to SharePoint 2016 on-premise.
This code sample shown here works in .NET 4.7, however it throws errors when run on .NET Core.
public async Task<string> UploadFile(string folderName, string fileName, byte[] file)
{
// Url to upload file
string resourceUrl = _sharePointUrl + $"/_api/web/GetFolderByServerRelativeUrl('/opportunity/{folderName}')/Files/add(url='{fileName}',overwrite=true)";
HttpWebRequest wreq = HttpWebRequest.Create(resourceUrl) as HttpWebRequest;
wreq.Credentials = _credentials;
wreq.Headers.Add("X-FORMS_BASED_AUTH_ACCEPTED", "f");
// Get formdigest value from site
wreq.Headers.Add("X-RequestDigest", GetFormDigest());
wreq.Headers.Add("binaryStringRequestBody", "true");
wreq.Method = "POST";
wreq.Accept = "application/json; odata=verbose";
wreq.ContentLength = file.Length;
wreq.Timeout = 100000;
await wreq.GetRequestStream().WriteAsync(file, 0, file.Length);
HttpWebResponse response = (HttpWebResponse)wreq.GetResponse();
return response.StatusDescription;
}
Errors are listed below. The errors are happening on the
HttpWebResponse response = (HttpWebResponse)wreq.GetResponse();
line.
System.AggregateException: 'One or more errors occurred. (An error occurred while sending the request.)'
Inner Exception 1: WebException: An error occurred while sending the request.
Inner Exception 2: HttpRequestException: An error occurred while sending the request.
Inner Exception 3: IOException: The response ended prematurely.
What am I missing?
Does the HttpWebRequest in .NET Core work differently than the .NET framework version?
Do I need to use different headers or configure the request object differently?
Thanks in advance.