You want a neat way to do exactly as you asked, to have a checkbox get checked when all the checkboxes in a column are checked? Or, more precisely, the instructions below will give you a cell that looks like a checkbox but is actually a TRUE/FALSE formula that is displayed as a checked/unchecked box.
- Select the cell(s) where you want the automatic checkbox
- Run the AppleScript given below. (Copy/paste it into the Script Editor app then hit the "play/run" button.) The result should be a checkbox but the cell will have a formula of =TRUE.
- Edit the cell's formula. The one I would use would be something like =COUNTIF(B,TRUE)=COUNTA(B) . This is like the condition in an IF statement. If the two counts are the same then the result will be true.
This is an undocumented "feature" so it may get "fixed" by Apple in the future. I recall this can be done in the iOS version without any scripts by simply formatting a cell as checkbox then entering a formula. So it could just be a non-implemented feature in the Mac version.
tell application "Numbers"
tell front document to tell active sheet
tell (first table whose selection range's class is range)
repeat with aCell in (get selection range)'s cells
set format of aCell to "checkbox"
set value of aCell to "=TRUE"
end repeat
end tell
end tell
end tell