You might have better success if you work with a native file (.ods) rather than a .xlsm file although in my tests it worked either way.
When you select the checkbox control, if you see the green handles surrounding it, as in your screen shot, then you are in the
Design Mode.On a spreadsheet you will need to use the
Form Design toolbar which is not normally visible on spreadsheets, so you may need to add it by selecting
View>Toolbars>Form Design. Near the left of the toolbar is the
Design Mode On/Off button.
The checkbox should work with the
Design Mode off.
New Calc users should also read this
[Tutorial] Ten concepts that every Calc user should know
If your problem has been solved, please edit this topic's initial post and add "[Solved]" to the beginning of the subject line
Apache OpenOffice 4.1.8 & LibreOffice 6.4.7.2 - Windows 10 Professional