Finding all checkboxes in a Google Sheet

Ever since checkboxes were added to the native Google Sheets UI in 2018, developers have wanted to programmatically read them or treat them in certain manners, such as treating them as "radio buttons", resetting them to "unchecked", or setting them to "checked".

How can we best find checkboxes in a given Google Sheet, so that we avoid accidentally modifying other cells when manipulating their state?

One method is to inspect the values on a worksheet and treat any true/false values as checkboxes:

function getAllCheckboxes() {
  const wb = SpreadsheetApp.getActive();
  const checkboxes = [];

  wb.getSheets().forEach(function (sheet) {
    var rg = sheet.getDataRange();
    var values = rg.getValues();
    var sheetCheckBoxes = [];

    values.forEach(function (row, r) {
      row.forEach(function (val, c) {
        // Checkbox values are stored as `false` (unchecked) and `true` (checked)
        if (val === false || val === true) {
          sheetCheckBoxes.push({
            rowIndex: r,
            colIndex: c,
            value: val,
            r1c1: "R" + (r+1) + "C" + (c+1)
          });
        }
      });
    });
    if (sheetCheckBoxes.length) {
      checkboxes.push({
        name: sheet.getName(),
        sheetId: sheet.getSheetId(),
        boxes: sheetCheckBoxes
      });
    }
  });

  return checkboxes; // An array of objects describing a sheet and its checkboxes.
}

However, this won't work in all use cases: the cell might be displayed as the literal TRUE or FALSE, and not as a checkbox. The above code will treat it as though it is one, because it shares the same value.