The error message tells that the variable
sheet does not refer to a sheet (tab) in the spreadsheet but to the whole spreadsheet.
.getRange('A1') method exists with both sheet and spreadsheet objects. With a spreadsheet object, the method gets a range in the sheet that shows as the first one in the tab bar of the spreadsheet. The
.getRange(1, 1) method, however, is only available with sheet objects.
To get a sheet object, use SpreadsheetApp.getActiveSheet() or similar methods, like this:
const sheet = SpreadsheetApp.getActiveSheet();