use

let formData = new FormData();
                formData.append('files', filePart);
                formData.append('chunk', index.toString());

pass parameters to the server and split the file.
Note: Google browser does not need to set content-type, or the backend will not get the data

then upload parts with ajax to see how the server configures

browser crashes and the interface times out. I wish I had changed the limit of nginx. Please refer to