Hello Emerson,
Your first function using CSV files does work and uploads as a list object in the cloud. For some strange reason I can't get the XLSX upload FormFunction to work. After submitting, the file name is removed and an error "upload a file of type XLSX" message appears in red. What could be the cause of this?
My main goal is to upload a xlsx file as is. No translation to list object. Is that easier? kind regards, Pieter

Thanks Emerson for your ideas. I am still looking for a way to upload XLS files via a webform. Does anyone have Ideas on how to upload a file via a webform.

Spend a day trying things like this:

CloudDeploy @
 FormFunction[
  "fname" -> "String", 
  Module[{st1, st2},
    st1 = "E:\\math9\\Personal Lessons\\" <> #fname <> ".xls";
    st2 = #fname <> ".xls";
    {st1, st2, CopyFile[st1, CloudObject[st2]]}
    ] &
  ]

CopyFile seems to work only from the desktop and not on a webform.

I also tried

CloudDeploy @
 FormFunction[
  "fname" -> Interpreter[Restricted["UploadedFile", "XLS"]],
  {#fname}
  ]

but it looks this does not work because it always produces the following error:

The function isn't even evaluated and I assure you the file submitted had the right type.

can anybody help on how to do this or state that it is not yet possible in the WolframCloud?

kind regards, Pieter van Bijnen