Am just getting back into working out and am planning on doing a 5day PPLPP at some point

I'm thinking I'll do first PP days with 12-15 sets per muscle group, 8-12 rep range, with very limited time between sets (2 mins-ish), potentially failure on each set.

Second PP of the week working more of a 5-5-3-1 kind of range, with long rests between sets (3-5mins).

I know noone lifts, but maybe some anecdotal experiences?

My current split is leg/pull, push, off, legs, pull, push, off, repeat. I typically work up to a heavy single, double or triple on my primary movement for the day, then hit 1-2 backdown sets with the same lift then move on to accessory/isolation movements.

Example push day -

Flat BB bench - work up to a heavy single, followed by a hard 5-8 rep set, then a lighter 12-20 repper.
DB incline press - 3 sets, 6-12 reps/set
Cable tri pressdown - 3×15ish
Band tri pulldown - 1-2×AMRAP
Cable face pull - 3×15ish

I have found this approach to be the best mix of maintaining/gaining strength as well as working in the hypertrophy rep ranges while still getting adequate recovery.

So you are combining high rep/low rep into one single push day. That's not my question at all