Uploaded file extension is always replaced

I’m trying to upload office files to collection, I tested different forms

{"custom-file": "https://url-to.pptx"}
{"custom-file": {url: "https://url-to.pptx"}}
{"custom-file": {url: "https://url-to.pptx", name: "file.pptx"}}
{"custom-file": {url: "https://url-to.pptx", name: "file.pptx", file: {name: "file.pptx", "mimeType": "application/vnd.openxmlformats-officedocument.presentationml.presentation",}}}

No matte what always the file ends as a DOCX

image

Any ideas the reason why this is happening

Sample file: https://uploads-ssl.webflow.com/623509b98f4c7408fadb35f1/62704e29d522c1ae6c496c43_samplepptx.pptx