I know there is a way to upload to S3 directly from the web browser using POST without the files going to your backend server. But is there a way to do it from URL instead o
It sounds like you want S3 itself to download the file from a remote server where you only pass the URL of the resource to S3.
This is not currently supported by S3.
It needs an API client to actually transfer the content of the object to S3.