Automatically scroll to the last row in a Google Sheets spreadsheet upon opening the file. Google Docs. Google Drive.

selectLastCell.gs

//
// Automatically scroll to the last row.
//
function selectLastRow() {
  const sheets = SpreadsheetApp.getActive().getSheets();
  
  // Set focus to the last active row on the first two sheets.
  for (var sheetIndex = 0; sheetIndex < 2; sheetIndex++) {
    // Get the sheet.
    var sheet = sheets[sheetIndex];
    
    // Set the active cell to the last cell in the first column.
    var range = sheet.getRange(sheet.getLastRow() + 1, 1);
    sheet.setActiveCell(range);
    
    // Update the sheet.
    SpreadsheetApp.flush();
  }
  
  // Set the first sheet as active.
  SpreadsheetApp.setActiveSheet(sheets[0]).getRange(sheets[0].getLastRow() + 1, 1).activate();
}

function onOpen() {
  selectLastRow();
}