You are likely looking at an incorrect assumption that you can exhaust all possible combinations uninterrupted, in a short period of time.
Which is incorrect because after 5 failed attempts, you are barred from entering PIN / password and a pause of 30 seconds is introduced before you try again or you would need to reset your phone to be able to use a new PIN. I am not sure how one plus implements this and may vary a little bit that's the standard expected behaviour called rate limiting. See my answers here and here
Note This answer was before the question was edited and Andy Yan's answer deals with çhanges made to question