For anyone who finds this, I was using ChatGPT and looking all around and had a nightmare of a time until I found this. My issue was the same, but I was using the pre-built standalone version and that used "FormData" to submit to SharePoint.

I was trying everything with Dropzone and kept getting corrupt files. My answer was to go to the github: https://github.com/dropzone/dropzone/tree/main

Then build it and use the built stand alone version. Then when I used it, I had to set the option "options.binaryBody" to true.

Once this was set to true, it no longer used "FormData", but now used the files parameter.

I wasn't able to find this documentation at all, but the pointer to look at the submitRequest was extremely helpful and hopefully this helps someone else.