80% is 7-8 solid reps, you can double check by using your current TM and the 1RM formula, which is: (weight x number of reps x 0,0333)+weight.
I.e. if your current TM on bench is 100kg, 85% (5 reps), your estimated 1RM is 116kg. 80% of it is 93kg.
If you use the formula putting the 80%TM (93kg) for 7 reps, it gives you an estimated 1RM of 114kg, for 8 reps it gives close to 118kg - both are give or take in line with the example estimated 1RM of 116kg.
You should have a good approximate idea of the number of reps you can get from your latest Anchor PR sets @95% of your current TM. It’s not bulletproof math but, give or take, 95% of an 85%TM equals to 80-81% of your 1RM. If you got at least 7-8 reps on that PR set, chances are that that’s your new TM since it’s in line with the 80% you need for 5x531.
If you got fewer reps (5-6) you probably better shoot for lowering the TM 1 cycle back in your TM test, which should get you 7-8 reps.
If you got less than 5 solid reps in your 95% week, it’s probably better to test the TM from scratch since you’ll probably have to take it back 2-3 cycles.
If you got more than 7-8 reps on your 1+ PR test, you could try increasing the TM as usual after the Anchor cycle, and test the increased one to see if you can get 7-8 reps. But I wouldn’t increase the TM more than the usual increase, even if you get a gazillion reps in the TM test.