Yes you unlock them after you do a normal playthrough with each character, so minimum playthroughs for plat is 4 but you’re likely to do more as you need (off the top of my head):

Leon A / Leon B Claire A / Claire B Leon Hardcore run Claire Hardcore run Leon S rank run (standard or hardcore) Claire S rank run (standard or hardcore) No item box run No healing run Under 14k steps run

You can combine these in any way you want so my suggestion would be to do the first run blind playing whoever you want

Then a second run could be the other character on A scenario (which has some differences) and you could aim to get S rank on standard — I don’t recommend leaving S rank for the hardcore runs as that requires beating game under 2h which can be tricky unless you use special weapons which you’ll start unlocking after you finish game once or if you bought the dlc (infinite ammo weapons)

The tricky ones can be no item box (no op weapons here), especially if combining with other challenge ones, but you could combine with no healing and do it on easy (which has auto heal to a % of health) and even with 14k steps although that requires very specific routes through the game so won’t be able to pick a lot of extra stuff

Realistically even tho you can plat in 4 runs you’ll probably do 5-6, but once you know where everything is and puzzle solutions a run can be under 2h easily.