Select the problem cell and open Data → Data validation. If there is no Checkbox rule, try Insert → Checkbox in an empty cell you can edit. If the box toggles but a formula still returns the wrong result, check what value the rule stores when the box is checked.
01Compare a missing box with a working one
Section linkPick an empty cell in an editable area and choose Insert → Checkbox. Click it to confirm it toggles. If that works, compare its data validation rule with the original cell’s rule. Reapply the intended rule to the affected range, preferably in a copy if the existing cell contains values you need to keep.
02Check permissions when the box won’t toggle
Section linkIf the box is visible but you cannot change it, try editing a blank cell that you know is editable. Viewers and commenters cannot toggle a checkbox. If you can edit elsewhere in the file, ask the owner or an editor to check whether the checkbox is in a protected sheet or range.
03Check the value a formula actually reads
Section linkAn ordinary checkbox uses TRUE when checked and FALSE when unchecked. A checkbox with custom values might store Yes and No instead. Check Use custom cell values in its validation rule. If a count or filter does not match what you see, compare the value it expects with the value the checkbox really writes, then toggle the box and check the result again.