Import a local xls to Google Sheets with Apps Script

You could upload a local XLS file using a pop-up prompt within your Google Sheet. Make sure you assign the script importExcel to a button or a menu option.

Here is a working script:

function importExcel(e) {

  if (!e) {
    SpreadsheetApp.getUi().showModalDialog(HtmlService.createHtmlOutputFromFile("uploadExcelpopup"), "Upload PIMMS Excel file");
    return;
  }

  var file = Utilities.newBlob(...e);

  let config = {
    title: "[Temporary Google Sheet] " + file.getName(),
    mimeType: MimeType.GOOGLE_SHEETS
  };
  let tempSs = Drive.Files.insert(config, file);

  var 
  fileId = tempSs.id,
  source = SpreadsheetApp.openById(fileId),
  sourceSheet = source.getSheets()[0];

    SpreadsheetApp.getActive().toast('Extracting data','🔄 File uploaded',10);

  var
  sourceValues = sourceSheet.getRange(1,1,sourceSheet.getLastRow(),sourceSheet.getLastColumn()).getValues(),
  sheetDataset = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Dataset");

  sheetDataset.getRange(1, 1, sourceValues.length, sourceValues[0].length).setValues(sourceValues);

  DriveApp.getFileById(fileId).setTrashed(true);

    SpreadsheetApp.getActive().toast('', '✔️ Upload complete',10);
    
}

You will also need to create an HTML file:

<form>
  <input type="file" name="file" onchange="importExcel(this.parentNode)" accept=".xls,.xlsx,.xlsm" id="inputFile" >
  <font face = "Calibri" size = "3"> <br><div id="progress">⏳ Waiting</div></font>
</form>
<script>
function importExcel(e) {
  const div = document.getElementById("progress");
  div.innerHTML = "🔄 Uploading";
  const file = e.file.files[0];
  const f = new FileReader();
  f.onload = d => google.script.run.withSuccessHandler(_ => {
    div.innerHTML = "✔️ Done";
    setTimeout(google.script.host.close, 1000);
  }).importExcel([[...new Int8Array(d.target.result)], file.type, file.name]);
  f.readAsArrayBuffer(file);
  
}
</script>

This is based on Tanaike's CSV local input pop-up suggestion:

Google Sheets Import CSV popup