DARQ: Complete Edition

In chapter 4, at the end when you pull the lever after the mask room and it opens the ground to your left, before going down use the ground lever right next to the hole and pull backwards, moving towards the screen. You will move up onto a ledge. Go down to the left and it will lead to a door you can open and inside is the journal.

If you are going back and collecting any journals you missed with chapter select, you do not have to finish the level to save it. You can immediately quit to the menu / choose a new chapter after picking it up.