how to disable all the remaining checkboxes while we select one in editable grid?

Can you elaborate more, you question ?

If you select one of the checkboxes and then immediately disable all of the others the only way the User can change their mind is to de-select the selected one and then select another option. That then leads me to think what you're really asking is how can we only restrict the selection to one option at a time? Would that be your actual requirement?

please use {a!save(<name of cdt>.isprimary ,null),a!save(<name of cdt>[ri!index].isprimary ,ri!Index)} under your checkbox field

It is by default available.