Last evening mocked up sort of a sample showing 2 methods of how to do this in Lectora Online.
One option is disabling your button(s)/element(s) in the interactivity/exercise after doing it once..the other is using conditions on it. Showing both in this package. Whether one of those fits your scenario i cannot say for certain. If not, i would need a sample of your setup in Lectora Online too, to check whether conditions or some other method is valid to get it to do what you want.
Well here it is.. 😉
Kind regards and enjoy your day,