No, PR sets are AMRAP sets… easy as that. You push the last sets for as many reps as possible, (trying) to get to a PR. The PR can be a rep PR or you can use the 1RM calculator and see if the result you just did is higher than previous week.
What you described is the very first iteration of Jokers in Beyond, where you added 5-10% increments after the last set trying to do the same reps as the base reps in the week (5 first week, 3 second, 1 third).
He asked what a ‘5/3/1, PR set’ is on Krypteia part 3, which was just going for as many reps as he can on his last 5/3/1 set of the week.
What you’ve described is something completely different: