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

The issue is not solved but I was able to generate error messages that may help a more knowledgeable person reading this (goal is upload XLS sheet via Wolfram Cloud Web Form Submit)

FormFunction[
  "fname" -> "String", 
  Module[{},
    st1 = "E:\\testfolder\\" <> #fname;
    st2 = #fname;
    SetCloudDirectory[$CloudRootDirectory];
    SetCloudDirectory["results"];
    zz = CloudObject[st2];
    {EvaluationData[CopyFile[st1, zz]]}
    ] &
  ][]

This (above) runs from the Mathematica desktop application (and works fine) and generates the following evaluation data:

{<|"Result" -> CloudObject[
   "https://www.wolframcloud.com/objects/user-9b714558-a731-4b6e-9313-\
00431f13aa06/results/xlsbook4.xls"], "Success" -> True, 
  "FailureType" -> None, "Messages" -> {}, "MessagesText" -> {}, 
  "MessagesExpressions" -> {}, "Timing" -> 1.076, 
  "AbsoluteTiming" -> 2.48, "InputString" -> "CopyFile[st1, zz]"|>}

The next example is extended with CloudDeploy and is NOT a success. See error message generated by webform:

--code --
CloudDeploy[FormFunction[
  "fname" -> "String", 
  Module[{},
    st1 = "E:\\testfolder\\" <> #fname;
    st2 = #fname;
    SetCloudDirectory[$CloudRootDirectory];
    SetCloudDirectory["results"];
    zz = CloudObject[st2];
    {EvaluationData[CopyFile[st1, zz]]}
    ] &
  ]]

(error message )

{<|"Result" -> $Failed, "Success" -> False, 
      "FailureType" -> "MessageFailure", 
      "Messages" -> {FileFormat::nffil, StringMatchQ::strse, 
        BinaryReadList::nffil, CloudObject::srverr}, 
      "MessagesText" -> {"FileFormat::nffil : File not found during \
    FileFormat[E:\\testfolder\\xlsbook4.xls].", 
        "StringMatchQ::strse : String or list of strings expected at \
    position 1 in StringMatchQ[$Failed, __~~/~~__].", 
        "BinaryReadList::nffil : File not found during \
    BinaryReadList[E:\\testfolder\\xlsbook4.xls].", 
        "CloudObject::srverr : An unknown server error occurred."}, 
      "MessagesExpressions" -> {Hold[
         Message[FileFormat::nffil, 
          HoldForm[FileFormat["E:\\testfolder\\xlsbook4.xls"]]]], 
        Hold[Message[StringMatchQ::strse, HoldForm[1], 
          HoldForm[StringMatchQ[$Failed, __ ~~ "/" ~~ __]]]], 
    Hold[Message[BinaryReadList::nffil, 
      HoldForm[BinaryReadList["E:\\testfolder\\xlsbook4.xls"]]]], 
    Hold[Message[CloudObject::srverr]]}, "Timing" -> 0.01, 
  "AbsoluteTiming" -> 0.01, "InputString" -> "CopyFile[st1, zz]"|>}

The code below is including the File[st1] command and seems to work a little better but still Success is false: ( looks like there is no access to the local disk anymore... but how to provide that access)

(* code *)

CloudDeploy[FormFunction[
  "fname" -> "String", 
  Module[{},
    st1 = "E:\\testfolder\\" <> #fname;
    st2 = #fname;
    SetCloudDirectory[$CloudRootDirectory];
    SetCloudDirectory["results"];
    zz = CloudObject[st2];
    {EvaluationData[CopyFile[File[st1], zz]]}
    ] &
  ]]

(* error data *)

{<|"Result" -> 
   CloudObject[
    "https://www.wolframcloud.com/objects/user-9b714558-a731-4b6e-\
9313-00431f13aa06/results/xlsbook5.xls"], "Success" -> False, 
  "FailureType" -> "MessageFailure", 
  "Messages" -> {StringMatchQ::strse, 
    "`1` is not a string, InputStream[ ], or OutputStream[ ]."}, 
  "MessagesText" -> {"StringMatchQ::strse : String or list of strings \
expected at position 1 in StringMatchQ[FileFormat[File[E:\\testfolder\
\\xlsbook5.xls]], __~~/~~__].", 
    "General::stream : File[E:\\testfolder\\xlsbook5.xls] is not a \
string, InputStream[ ], or OutputStream[ ]."}, 
  "MessagesExpressions" -> {Hold[
     Message[StringMatchQ::strse, HoldForm[1], 
      HoldForm[
       StringMatchQ[
        FileFormat[File["E:\\testfolder\\xlsbook5.xls"]], __ ~~ 
         "/" ~~ __]]]], 
    Hold[Message[General::stream, 
      HoldForm[File["E:\\testfolder\\xlsbook5.xls"]]]]}, 
  "Timing" -> 1.0230000000000001, "AbsoluteTiming" -> 1.27, 
  "InputString" -> "CopyFile[File[st1], zz]"|>}

hope this info helps with ideas on how to resolve this issue. Kind Regards, pvanbijnen.

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